diff --git a/.github/workflows/push.yml b/.github/workflows/push.yml
index c4323141e..b5e575509 100644
--- a/.github/workflows/push.yml
+++ b/.github/workflows/push.yml
@@ -82,6 +82,7 @@ jobs:
                     - { name: "SpeakerSubmitterPublishedFilter", filter: "tests/ProcessSpeakersEmailRequestJobTest.php tests/ProcessSubmittersEmailRequestJobTest.php tests/SpeakerRepositoryTest.php tests/SubmitterRepositoryTest.php tests/SpeakerServiceOriginalFilterTest.php tests/SubmitterServiceOriginalFilterTest.php" }
                     - { name: "SpeakerBulkEmailChunkResume", filter: "tests/SpeakerServiceBulkSendChunkingTest.php tests/SpeakerServiceResumeSendEmailsTest.php tests/ProcessSpeakersEmailRequestJobResumeTest.php tests/ProcessSpeakersEmailRequestJobFailedHookTest.php" }
                     - { name: "AttendeeBulkEmailChunkResume", filter: "tests/AttendeeServiceBulkSendChunkingTest.php tests/AttendeeServiceResumeSendEmailsTest.php tests/ProcessAttendeesEmailRequestJobResumeTest.php tests/ProcessAttendeesEmailRequestJobFailedHookTest.php tests/SummitAttendeeAnnouncementEmailTest.php tests/DoctrineSummitAttendeeRepositoryTest.php tests/SummitExtraQuestionsMemoizationTest.php" }
+                    - { name: "AttendeeMemberEmailConflict", filter: "tests/AttendeeMemberEmailConflictTest.php" }
                     - { name: "SummitJsonGenerator", filter: "tests/SummitJsonGeneratorCommandTest.php" }
                     - { name: "Repositories", filter: "tests/Repositories/" }
                     - { name: "Services", filter: "tests/Unit/Services/" }
diff --git a/app/Console/Commands/RepairAttendeeMemberEmailPairsCommand.php b/app/Console/Commands/RepairAttendeeMemberEmailPairsCommand.php
new file mode 100644
index 000000000..b9f7b8ec6
--- /dev/null
+++ b/app/Console/Commands/RepairAttendeeMemberEmailPairsCommand.php
@@ -0,0 +1,142 @@
+<?php namespace App\Console\Commands;
+/**
+ * Copyright 2026 OpenStack Foundation
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ **/
+use App\Jobs\UpdateAttendeeInfo;
+use App\Jobs\Utils\JobDispatcher;
+use Illuminate\Console\Command;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Log;
+
+/**
+ * Class RepairAttendeeMemberEmailPairsCommand
+ *
+ * A pair is an attendee linked to a member whose email differs from the member's current one,
+ * plus another attendee of the same summit with no member that already has the member's email.
+ * Only UpdateAttendeeInfo merges a pair, and only when the member's email is verified.
+ *
+ * Without --dispatch it only reads: run it before and after the repair.
+ * @package App\Console\Commands
+ */
+class RepairAttendeeMemberEmailPairsCommand extends Command
+{
+    /**
+     * @var string
+     */
+    protected $name = 'summit:repair-attendee-member-email-pairs';
+
+    /**
+     * @var string
+     */
+    protected $signature = 'summit:repair-attendee-member-email-pairs {--dispatch : enqueue UpdateAttendeeInfo for each member of a pair with a verified email} {--limit= : dispatch at most this many members} {--after-member-id= : only dispatch members with an id greater than this one, to resume after the last dispatched member}';
+
+    /**
+     * @var string
+     */
+    protected $description = 'Lists the attendee/member email pairs and dispatches UpdateAttendeeInfo for the ones with a verified email';
+
+    /**
+     * @return array
+     */
+    private function getPairs(): array
+    {
+        return DB::connection('model')->select(<<<'SQL'
+SELECT
+    a.SummitID                  AS summit_id,
+    m.ID                        AS member_id,
+    m.EmailVerified             AS email_verified,
+    a.ID                        AS attendee_id,
+    b.ID                        AS memberless_attendee_id
+FROM SummitAttendee a
+JOIN Member m ON m.ID = a.MemberID
+JOIN SummitAttendee b
+    ON b.SummitID = a.SummitID AND b.MemberID IS NULL AND b.Email = m.Email
+WHERE NOT (a.Email <=> m.Email)
+ORDER BY a.SummitID, m.EmailVerified DESC, m.ID
+SQL
+        );
+    }
+
+    /**
+     * @return int
+     */
+    public function handle(): int
+    {
+        $pairs = $this->getPairs();
+
+        $groups = [];
+        foreach ($pairs as $pair) {
+            $key = sprintf("%s|%s", $pair->summit_id, $pair->email_verified);
+            $groups[$key] = ($groups[$key] ?? 0) + 1;
+        }
+        ksort($groups);
+
+        $this->info(sprintf("%s pairs", count($pairs)));
+        $rows = [];
+        foreach ($groups as $key => $count) {
+            [$summit_id, $verified] = explode('|', $key);
+            $rows[] = [$summit_id, $verified ? 'yes' : 'no', $count];
+        }
+        $this->table(['summit_id', 'member email verified', 'pairs'], $rows);
+
+        // ids only, no emails: enough to inspect the attendees and to follow up on the unverified ones
+        $detail = [];
+        foreach ($pairs as $pair) {
+            $detail[] = [
+                $pair->summit_id,
+                $pair->member_id,
+                $pair->email_verified ? 'yes' : 'no',
+                $pair->attendee_id,
+                $pair->memberless_attendee_id,
+            ];
+        }
+        $this->table(['summit_id', 'member_id', 'member email verified', 'attendee_id', 'member-less attendee_id'], $detail);
+
+        if (!$this->option('dispatch')) {
+            $this->line('Dry run, nothing dispatched. Use --dispatch to enqueue UpdateAttendeeInfo for the verified ones.');
+            return 0;
+        }
+
+        // one job per member: it updates the member's attendees in every summit
+        $member_ids = [];
+        foreach ($pairs as $pair) {
+            if (!$pair->email_verified) continue;
+            $member_ids[(int)$pair->member_id] = true;
+        }
+        $member_ids = array_keys($member_ids);
+        // stable order, so --after-member-id can resume past a member whose job keeps failing
+        sort($member_ids);
+
+        $after_member_id = $this->option('after-member-id');
+        if (!is_null($after_member_id) && $after_member_id !== '') {
+            $after_member_id = intval($after_member_id);
+            $member_ids = array_values(array_filter($member_ids, fn(int $id) => $id > $after_member_id));
+        }
+
+        $limit = $this->option('limit');
+        if (!is_null($limit) && $limit !== '')
+            $member_ids = array_slice($member_ids, 0, max(0, intval($limit)));
+
+        foreach ($member_ids as $member_id) {
+            Log::info(sprintf("RepairAttendeeMemberEmailPairsCommand dispatching UpdateAttendeeInfo member id %s", $member_id));
+            JobDispatcher::withDbFallback(
+                job: new UpdateAttendeeInfo($member_id),
+                logContext: ['member_id' => $member_id]
+            );
+        }
+
+        $this->info(sprintf("dispatched UpdateAttendeeInfo for %s members", count($member_ids)));
+        if (count($member_ids))
+            $this->line(sprintf("last member id dispatched: %s (resume with --after-member-id=%s)", end($member_ids), end($member_ids)));
+        return 0;
+    }
+}
diff --git a/app/Console/Kernel.php b/app/Console/Kernel.php
index b0d15b21a..8c3ffe0e6 100644
--- a/app/Console/Kernel.php
+++ b/app/Console/Kernel.php
@@ -42,6 +42,7 @@ class Kernel extends ConsoleKernel
         \App\Console\Commands\SummitEmailFlowTypeSeederCommand::class,
         \App\Console\Commands\PresentationMaterialsCreateMUXAssetsCommand::class,
         \App\Console\Commands\RecalculateAttendeesStatusCommand::class,
+        \App\Console\Commands\RepairAttendeeMemberEmailPairsCommand::class,
         \App\Console\Commands\EnableMP4SupportAtMUXCommand::class,
         \App\Console\Commands\SummitMediaUploadMigratePrivateToPublicStorage::class,
         \App\Console\Commands\PresentationMediaUploadsRegenerateTemporalLinks::class,
diff --git a/app/Models/Foundation/Summit/Repositories/ISummitAttendeeRepository.php b/app/Models/Foundation/Summit/Repositories/ISummitAttendeeRepository.php
index e3d9237ca..7441faff0 100644
--- a/app/Models/Foundation/Summit/Repositories/ISummitAttendeeRepository.php
+++ b/app/Models/Foundation/Summit/Repositories/ISummitAttendeeRepository.php
@@ -73,6 +73,15 @@ public function getByEmail(string $email);
      */
     public function getByEmailAndMemberNotSet(string $email);
 
+    /**
+     * Member-less attendees with the member's email that can be linked to the member, that is, the
+     * ones in summits where the member has no attendee yet (SummitAttendee_Member_Summit allows one).
+     * Logs a warning for each skipped summit.
+     * @param Member $member
+     * @return SummitAttendee[]
+     */
+    public function getLinkableByMember(Member $member): array;
+
     /**
      * @param Summit $summit
      * @param null|string $external_id
diff --git a/app/Repositories/Summit/DoctrineSummitAttendeeRepository.php b/app/Repositories/Summit/DoctrineSummitAttendeeRepository.php
index dc7dfe05d..1b876a168 100644
--- a/app/Repositories/Summit/DoctrineSummitAttendeeRepository.php
+++ b/app/Repositories/Summit/DoctrineSummitAttendeeRepository.php
@@ -430,6 +430,36 @@ public function getByEmailAndMemberNotSet(string $email)
         return $query->getQuery()->getResult();
     }
 
+    /**
+     * @param Member $member
+     * @return SummitAttendee[]
+     */
+    public function getLinkableByMember(Member $member): array
+    {
+        $res = [];
+        foreach ($this->getByEmailAndMemberNotSet($member->getEmail()) as $attendee) {
+            if (!$attendee instanceof SummitAttendee) continue;
+            $summit = $attendee->getSummit();
+            $member_attendee = $summit->getAttendeeByMember($member);
+            if (!is_null($member_attendee)) {
+                Log::warning
+                (
+                    sprintf
+                    (
+                        "DoctrineSummitAttendeeRepository::getLinkableByMember member %s already has attendee %s in summit %s, skipping member-less attendee %s.",
+                        $member->getId(),
+                        $member_attendee->getId(),
+                        $summit->getId(),
+                        $attendee->getId()
+                    )
+                );
+                continue;
+            }
+            $res[] = $attendee;
+        }
+        return $res;
+    }
+
     /**
      * @param Summit $summit
      * @param string $email
diff --git a/app/Services/Model/AttendeeService.php b/app/Services/Model/AttendeeService.php
index b0dee3d57..b54175e79 100644
--- a/app/Services/Model/AttendeeService.php
+++ b/app/Services/Model/AttendeeService.php
@@ -982,49 +982,77 @@ public function updateAttendeesByMemberId(int $member_id): void
                     $summit = $attendee->getSummit();
                     if (!$summit instanceof Summit) continue;
 
-                    // check if we have an attendee without member set and with same email
-                    $attendee_without_member = $summit->getAttendeeByEmailAndMemberNotSet($email);
+                    // check if the email is already taken by another attendee of the summit
+                    $attendee_with_email = $summit->getAttendeeByEmail($email);
+                    $update_email = true;
 
-                    if (!is_null($attendee_without_member) && $member->isEmailVerified()) {
+                    if (!is_null($attendee_with_email) && $attendee_with_email->getId() != $attendee->getId()) {
 
-                        Log::debug
-                        (
-                            sprintf
+                        $attendee_without_member = $summit->getAttendeeByEmailAndMemberNotSet($email);
+
+                        if (!is_null($attendee_without_member) && $member->isEmailVerified()) {
+
+                            Log::debug
                             (
-                                "AttendeeService::updateAttendeesByMemberId found attendee %s with email %s and member not set ( marking it for deletion ).",
-                                $attendee_without_member->getId(),
-                                $attendee_without_member->getEmail()
-                            )
-                        );
+                                sprintf
+                                (
+                                    "AttendeeService::updateAttendeesByMemberId found attendee %s with email %s and member not set ( marking it for deletion ).",
+                                    $attendee_without_member->getId(),
+                                    $attendee_without_member->getEmail()
+                                )
+                            );
 
-                        // mark the attendee to be deleted bc its dupe
+                            // mark the attendee to be deleted bc its dupe
 
-                        $attendees_2_delete[] = $attendee_without_member->getId();
+                            $attendees_2_delete[] = $attendee_without_member->getId();
 
-                        // overwrite email to avoid FK exception
-                        $attendee_without_member->setEmail($attendee_without_member->getEmail() . '-deleted');
+                            // overwrite email to avoid unique key exception: unique per attendee and
+                            // always fits SummitAttendee.Email (varchar 100), unlike email + suffix
+                            $attendee_without_member->setEmail(sprintf("%s-deleted", $attendee_without_member->getId()));
+                            // flush now: Doctrine runs the UPDATEs in the order the entities were loaded,
+                            // and the member's attendee was loaded first, so it would take the email
+                            // while this row still has it.
+                            $this->attendee_repository->add($attendee_without_member, true);
 
-                        // check if we have ticket and re-assign them
-                        if ($attendee_without_member->hasTickets()) {
-                            foreach ($attendee_without_member->getTickets() as $ticket) {
-                                Log::debug
-                                (
-                                    sprintf
+                            // check if we have ticket and re-assign them
+                            if ($attendee_without_member->hasTickets()) {
+                                foreach ($attendee_without_member->getTickets() as $ticket) {
+                                    Log::debug
                                     (
-                                        "AttendeeService::updateAttendeesByMemberId re-assigning ticket %s from attendee %s to attendee %s",
-                                        $ticket->getId(),
-                                        $attendee_without_member->getId(),
-                                        $attendee->getId()
-                                    )
-                                );
-                                $attendee->addTicket($ticket);
+                                        sprintf
+                                        (
+                                            "AttendeeService::updateAttendeesByMemberId re-assigning ticket %s from attendee %s to attendee %s",
+                                            $ticket->getId(),
+                                            $attendee_without_member->getId(),
+                                            $attendee->getId()
+                                        )
+                                    );
+                                    $attendee->addTicket($ticket);
+                                }
                             }
+                        } else {
+                            $update_email = false;
+                            Log::warning
+                            (
+                                sprintf
+                                (
+                                    "AttendeeService::updateAttendeesByMemberId can not update the email of attendee %s of member %s in summit %s: the new email belongs to attendee %s (member %s, email verified %s), keeping attendee email.",
+                                    $attendee->getId(),
+                                    $member_id,
+                                    $summit->getId(),
+                                    $attendee_with_email->getId(),
+                                    $attendee_with_email->hasMember() ? $attendee_with_email->getMemberId() : 'none',
+                                    $member->isEmailVerified() ? 'yes' : 'no'
+                                )
+                            );
                         }
                     }
 
                     $attendee->setFirstName($fname);
                     $attendee->setSurname($lname);
-                    $attendee->setEmail($email);
+
+                    if ($update_email)
+                        $attendee->setEmail($email);
 
                     // company logic
 
@@ -1076,11 +1104,10 @@ public function updateAttendeesByMemberId(int $member_id): void
             $email = $member->getEmail();
             $company_name = $member->getCompany();
 
-            $attendees = $this->attendee_repository->getByEmailAndMemberNotSet($member->getEmail());
+            $attendees = $this->attendee_repository->getLinkableByMember($member);
             if (!is_null($attendees)) {
 
                     foreach ($attendees as $attendee) {
-                        if (!$attendee instanceof SummitAttendee) continue;
 
                         Log::debug
                         (
diff --git a/app/Services/Model/Imp/MemberService.php b/app/Services/Model/Imp/MemberService.php
index 60a57cff0..c8e254509 100644
--- a/app/Services/Model/Imp/MemberService.php
+++ b/app/Services/Model/Imp/MemberService.php
@@ -41,7 +41,6 @@
 use models\summit\ISpeakerRegistrationRequestRepository;
 use models\summit\ISummitAttendeeRepository;
 use models\summit\Presentation;
-use models\summit\SummitAttendee;
 use models\summit\SummitOrder;
 use function Psy\debug;
 
@@ -766,13 +765,9 @@ public function assocSummitOrders(int $member_id):void{
         $this->tx_service->transaction(function() use($member_id){
             // associate attendees/tickets
             $member = $this->member_repository->getById($member_id);
-            $attendees = $this->attendee_repository->getByEmailAndMemberNotSet($member->getEmail());
-            if(!is_null($attendees)) {
-                foreach ($attendees as $attendee) {
-                    if (!$attendee instanceof SummitAttendee) continue;
-                    Log::debug(sprintf("MemberService::assocSummitOrders got attendee %s for member %s", $attendee->getId(), $member_id));
-                    $attendee->setMember($member);
-                }
+            foreach ($this->attendee_repository->getLinkableByMember($member) as $attendee) {
+                Log::debug(sprintf("MemberService::assocSummitOrders got attendee %s for member %s", $attendee->getId(), $member_id));
+                $attendee->setMember($member);
             }
         });
     }
diff --git a/app/Services/Model/Imp/SummitOrderService.php b/app/Services/Model/Imp/SummitOrderService.php
index 9f490a955..11e5ae1d3 100644
--- a/app/Services/Model/Imp/SummitOrderService.php
+++ b/app/Services/Model/Imp/SummitOrderService.php
@@ -2262,6 +2262,32 @@ public function ownerAssignTicket(Member $current_user, int $order_id, int $tick
                 $attendee = $summit->getAttendeeByMember($member);
             }
 
+            if (!is_null($member) && !is_null($attendee)) {
+                // the member can have only one attendee per summit
+                $member_attendee = $summit->getAttendeeByMember($member);
+                if (!is_null($member_attendee) && $member_attendee->getId() != $attendee->getId()) {
+                    Log::warning
+                    (
+                        sprintf
+                        (
+                            "SummitOrderService::ownerAssignTicket the email belongs to member %s that already has attendee %s in summit %s, attendee found by email is %s.",
+                            $member->getId(),
+                            $member_attendee->getId(),
+                            $summit->getId(),
+                            $attendee->getId()
+                        )
+                    );
+                    throw new ValidationException
+                    (
+                        sprintf
+                        (
+                            "Email %s belongs to a member that already has an attendee in this summit.",
+                            $email
+                        )
+                    );
+                }
+            }
+
             if (is_null($attendee)) {
                 // if attendee did not exists... create a new one
                 Log::debug
diff --git a/tests/AttendeeMemberEmailConflictTest.php b/tests/AttendeeMemberEmailConflictTest.php
new file mode 100644
index 000000000..79185d8e0
--- /dev/null
+++ b/tests/AttendeeMemberEmailConflictTest.php
@@ -0,0 +1,286 @@
+<?php namespace Tests;
+/**
+ * Copyright 2026 OpenStack Foundation
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ **/
+
+use App\Models\Foundation\Main\IGroup;
+use App\Services\Model\IAttendeeService;
+use App\Services\Model\IMemberService;
+use Doctrine\DBAL\Connection;
+use App\Jobs\UpdateAttendeeInfo;
+use Illuminate\Support\Facades\App;
+use Illuminate\Support\Facades\Artisan;
+use Illuminate\Support\Facades\Bus;
+use LaravelDoctrine\ORM\Facades\Registry;
+use models\main\Member;
+use models\summit\SummitAttendee;
+use models\summit\SummitAttendeeNote;
+use models\utils\SilverstripeBaseModel;
+
+/**
+ * Class AttendeeMemberEmailConflictTest
+ *
+ * A member's email changes to the email of a member-less attendee of the same summit, so the
+ * member's attendee (old email) and the member-less one (new email) can not be reconciled
+ * without hitting SummitAttendee_Email_SummitID / SummitAttendee_Member_Summit.
+ */
+final class AttendeeMemberEmailConflictTest extends TestCase
+{
+    use InsertSummitTestData;
+
+    use InsertMemberTestData;
+
+    private const MemberlessEmail = 'memberless@test.com';
+
+    private const NewFirstName = 'Renamed';
+
+    private string $old_email;
+
+    private int $member_attendee_id;
+
+    private int $memberless_attendee_id;
+
+    private int $note_id;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        self::insertMemberTestData(IGroup::TrackChairs);
+        self::$defaultMember = self::$member;
+        self::insertSummitTestData();
+
+        $em = $this->em();
+        $this->old_email = self::$member->getEmail();
+
+        $member_attendee = self::$summit->getAttendeeByMember(self::$member);
+        $memberless_attendee = self::$summit->getAttendeeByEmailAndMemberNotSet(self::MemberlessEmail);
+        $this->assertNotNull($member_attendee);
+        $this->assertNotNull($memberless_attendee);
+
+        $note = new SummitAttendeeNote('Note on the member-less attendee', $memberless_attendee);
+        $memberless_attendee->addNote($note);
+        $em->persist($note);
+        $em->flush();
+
+        $this->member_attendee_id = $member_attendee->getId();
+        $this->memberless_attendee_id = $memberless_attendee->getId();
+        $this->note_id = $note->getId();
+    }
+
+    protected function tearDown(): void
+    {
+        self::clearSummitTestData();
+        self::clearMemberTestData();
+        parent::tearDown();
+    }
+
+    private function em(): \Doctrine\ORM\EntityManagerInterface
+    {
+        $em = Registry::getManager(SilverstripeBaseModel::EntityManager);
+        if (!$em->isOpen()) {
+            $em = Registry::resetManager(SilverstripeBaseModel::EntityManager);
+        }
+        return $em;
+    }
+
+    private function db(): Connection
+    {
+        return $this->em()->getConnection();
+    }
+
+    /**
+     * the member email changes to the member-less attendee's one and the first name changes too
+     */
+    private function changeMemberEmail(bool $verified, string $email = self::MemberlessEmail): void
+    {
+        $em = $this->em();
+        $member = $em->getRepository(Member::class)->find(self::$member->getId());
+        $member->setEmail($email);
+        $member->setEmailVerified($verified);
+        $member->setFirstName(self::NewFirstName);
+        $em->flush();
+        $em->clear();
+    }
+
+    private function attendeeRow(int $id): array|false
+    {
+        return $this->db()->fetchAssociative(
+            'SELECT ID, Email, FirstName, MemberID FROM SummitAttendee WHERE ID = ?',
+            [$id]
+        );
+    }
+
+    private function ticketsCount(int $attendee_id): int
+    {
+        return (int)$this->db()->fetchOne('SELECT COUNT(ID) FROM SummitAttendeeTicket WHERE OwnerID = ?', [$attendee_id]);
+    }
+
+    private function assertMemberAttendeeKeptOldEmail(): void
+    {
+        $row = $this->attendeeRow($this->member_attendee_id);
+        $this->assertEquals($this->old_email, $row['Email']);
+        $this->assertEquals(self::NewFirstName, $row['FirstName']);
+        $this->assertEquals(self::$member->getId(), $row['MemberID']);
+    }
+
+    public function testUpdateAttendeesByMemberIdVerifiedEmailMergesMemberlessAttendee(): void
+    {
+        $this->changeMemberEmail(true);
+
+        App::make(IAttendeeService::class)->updateAttendeesByMemberId(self::$member->getId());
+
+        $rows = $this->db()->fetchAllAssociative(
+            'SELECT ID, MemberID, FirstName FROM SummitAttendee WHERE SummitID = ? AND Email = ?',
+            [self::$summit->getId(), self::MemberlessEmail]
+        );
+        $this->assertCount(1, $rows);
+        $this->assertEquals($this->member_attendee_id, $rows[0]['ID']);
+        $this->assertEquals(self::$member->getId(), $rows[0]['MemberID']);
+        $this->assertEquals(self::NewFirstName, $rows[0]['FirstName']);
+        // its own 5 plus the member-less attendee's 1
+        $this->assertEquals(6, $this->ticketsCount($this->member_attendee_id));
+
+        $this->assertFalse($this->attendeeRow($this->memberless_attendee_id));
+        $this->assertEquals(
+            0,
+            (int)$this->db()->fetchOne('SELECT COUNT(ID) FROM SummitAttendeeNote WHERE ID = ?', [$this->note_id])
+        );
+    }
+
+    public function testUpdateAttendeesByMemberIdUnverifiedEmailKeepsBothAttendees(): void
+    {
+        $this->changeMemberEmail(false);
+
+        App::make(IAttendeeService::class)->updateAttendeesByMemberId(self::$member->getId());
+
+        $this->assertMemberAttendeeKeptOldEmail();
+
+        $row = $this->attendeeRow($this->memberless_attendee_id);
+        $this->assertEquals(self::MemberlessEmail, $row['Email']);
+        $this->assertNull($row['MemberID']);
+        $this->assertEquals(1, $this->ticketsCount($this->memberless_attendee_id));
+    }
+
+    public function testUpdateAttendeesByMemberIdEmailOwnedByAnotherMemberLeavesThatAttendeeUnchanged(): void
+    {
+        // the attendee that has the email belongs to another member
+        $this->db()->executeStatement(
+            'UPDATE SummitAttendee SET MemberID = ? WHERE ID = ?',
+            [self::$member2->getId(), $this->memberless_attendee_id]
+        );
+        $before = $this->attendeeRow($this->memberless_attendee_id);
+
+        $this->changeMemberEmail(true);
+
+        App::make(IAttendeeService::class)->updateAttendeesByMemberId(self::$member->getId());
+
+        $this->assertMemberAttendeeKeptOldEmail();
+        $this->assertEquals($before, $this->attendeeRow($this->memberless_attendee_id));
+        $this->assertEquals(1, $this->ticketsCount($this->memberless_attendee_id));
+    }
+
+    public function testAssocSummitOrdersDoesNotLinkMemberlessAttendeeToMemberWithAttendee(): void
+    {
+        $this->changeMemberEmail(true);
+
+        App::make(IMemberService::class)->assocSummitOrders(self::$member->getId());
+
+        $row = $this->attendeeRow($this->memberless_attendee_id);
+        $this->assertNotFalse($row);
+        $this->assertNull($row['MemberID']);
+        $this->assertEquals($this->old_email, $this->attendeeRow($this->member_attendee_id)['Email']);
+    }
+
+    public function testRepairCommandDispatchesOnlyVerifiedMembers(): void
+    {
+        $this->changeMemberEmail(true);
+        Bus::fake();
+
+        // dry run: lists the pair, dispatches nothing
+        Artisan::call('summit:repair-attendee-member-email-pairs');
+        $this->assertStringContainsString('1 pairs', Artisan::output());
+        Bus::assertNotDispatched(UpdateAttendeeInfo::class);
+
+        Artisan::call('summit:repair-attendee-member-email-pairs', ['--dispatch' => true]);
+        $member_id = self::$member->getId();
+        Bus::assertDispatched(UpdateAttendeeInfo::class, function (UpdateAttendeeInfo $job) use ($member_id) {
+            return (fn() => $this->member_id)->call($job) == $member_id;
+        });
+        Bus::assertDispatchedTimes(UpdateAttendeeInfo::class, 1);
+    }
+
+    public function testRepairCommandSkipsUnverifiedMembers(): void
+    {
+        $this->changeMemberEmail(false);
+        Bus::fake();
+
+        Artisan::call('summit:repair-attendee-member-email-pairs', ['--dispatch' => true]);
+
+        $this->assertStringContainsString('1 pairs', Artisan::output());
+        Bus::assertNotDispatched(UpdateAttendeeInfo::class);
+    }
+
+    public function testRepairCommandListsPairIdentifiers(): void
+    {
+        $this->changeMemberEmail(false);
+
+        Artisan::call('summit:repair-attendee-member-email-pairs');
+        $output = Artisan::output();
+
+        $this->assertStringContainsString((string)$this->member_attendee_id, $output);
+        $this->assertStringContainsString((string)$this->memberless_attendee_id, $output);
+        $this->assertStringNotContainsString(self::MemberlessEmail, $output);
+    }
+
+    public function testRepairCommandResumesAfterMemberId(): void
+    {
+        $this->changeMemberEmail(true);
+        Bus::fake();
+
+        // the member is at or before the cursor: skipped
+        Artisan::call('summit:repair-attendee-member-email-pairs', [
+            '--dispatch' => true,
+            '--after-member-id' => self::$member->getId(),
+        ]);
+        Bus::assertNotDispatched(UpdateAttendeeInfo::class);
+
+        Artisan::call('summit:repair-attendee-member-email-pairs', [
+            '--dispatch' => true,
+            '--after-member-id' => self::$member->getId() - 1,
+        ]);
+        Bus::assertDispatchedTimes(UpdateAttendeeInfo::class, 1);
+        $this->assertStringContainsString(
+            sprintf('--after-member-id=%s', self::$member->getId()),
+            Artisan::output()
+        );
+    }
+
+    public function testUpdateAttendeesByMemberIdMergesMemberlessAttendeeWithEmailNearColumnLimit(): void
+    {
+        // SummitAttendee.Email is varchar(100): email + "-deleted" would not fit
+        $long_email = str_repeat('a', 98 - strlen('@test.com')) . '@test.com';
+        $this->assertEquals(98, strlen($long_email));
+        $this->db()->executeStatement(
+            'UPDATE SummitAttendee SET Email = ? WHERE ID = ?',
+            [$long_email, $this->memberless_attendee_id]
+        );
+        $this->changeMemberEmail(true, $long_email);
+
+        App::make(IAttendeeService::class)->updateAttendeesByMemberId(self::$member->getId());
+
+        $this->assertFalse($this->attendeeRow($this->memberless_attendee_id));
+        $row = $this->attendeeRow($this->member_attendee_id);
+        $this->assertEquals($long_email, $row['Email']);
+        $this->assertEquals(6, $this->ticketsCount($this->member_attendee_id));
+    }
+}
diff --git a/tests/oauth2/OAuth2SummitTicketsApiTest.php b/tests/oauth2/OAuth2SummitTicketsApiTest.php
index 555617c4a..04b119edf 100644
--- a/tests/oauth2/OAuth2SummitTicketsApiTest.php
+++ b/tests/oauth2/OAuth2SummitTicketsApiTest.php
@@ -21,6 +21,7 @@
 use Mockery;
 use models\summit\IPaymentConstants;
 use models\summit\PaymentGatewayProfileFactory;
+use models\summit\SummitAttendee;
 
 /**
  * Class OAuth2SummitTicketsApiTest
@@ -1542,6 +1543,112 @@ public function testAssignAttendee()
         return $ticket;
     }
 
+    /**
+     * member2 has its own attendee in the summit and its email changes to the email of the
+     * member-less attendee, so assigning a ticket to that email would link two attendees
+     * of the same summit to member2.
+     */
+    private function assignTicketToEmailOfMemberOwningAnotherAttendee(bool $member_email_verified): void
+    {
+        $memberless_email = 'memberless@test.com';
+
+        $ticket = self::$summit_orders[0]->getFirstTicket();
+        $order = $ticket->getOrder();
+        $order->setOwner(self::$member);
+        self::$member->addSummitRegistrationOrder($order);
+
+        $member2_attendee = new SummitAttendee();
+        $member2_attendee->setMember(self::$member2);
+        $member2_attendee->setEmail(self::$member2->getEmail());
+        $member2_attendee->setFirstName(self::$member2->getFirstName());
+        $member2_attendee->setSurname(self::$member2->getLastName());
+        self::$summit->addAttendee($member2_attendee);
+
+        $member2_original_email = self::$member2->getEmail();
+        $member2_original_verified = self::$member2->isEmailVerified();
+        self::$member2->setEmail($memberless_email);
+        self::$member2->setEmailVerified($member_email_verified);
+        self::$em->persist($order);
+        self::$em->flush();
+
+        try {
+            $this->assertAssignAttendeeRejected($order, $ticket, $member2_attendee, $memberless_email);
+        } finally {
+            // Member.Email is unique and this class does not clear the members between tests;
+            // plain SQL because the entity manager is closed after a failed request
+            self::$em->getConnection()->executeStatement(
+                'UPDATE Member SET Email = ?, EmailVerified = ? WHERE ID = ?',
+                [$member2_original_email, (int)$member2_original_verified, self::$member2->getId()]
+            );
+        }
+    }
+
+    private function assertAssignAttendeeRejected($order, $ticket, SummitAttendee $member2_attendee, string $memberless_email): void
+    {
+
+        $memberless_attendee = self::$summit->getAttendeeByEmailAndMemberNotSet($memberless_email);
+        $this->assertNotNull($memberless_attendee);
+        $memberless_attendee_id = $memberless_attendee->getId();
+        $db = self::$em->getConnection();
+        $member2_attendee_email = $db->fetchOne('SELECT Email FROM SummitAttendee WHERE ID = ?', [$member2_attendee->getId()]);
+        $attendees_count = $db->fetchOne('SELECT COUNT(ID) FROM SummitAttendee WHERE SummitID = ?', [self::$summit->getId()]);
+        $tickets_count = $db->fetchOne('SELECT COUNT(ID) FROM SummitAttendeeTicket WHERE OwnerID = ?', [$memberless_attendee_id]);
+
+        $response = $this->action(
+            "PUT",
+            "OAuth2SummitOrdersApiController@assignAttendee",
+            [
+                'order_id' => $order->getId(),
+                'ticket_id' => $ticket->getId(),
+            ],
+            [],
+            [],
+            [],
+            [
+                "HTTP_Authorization" => " Bearer " . $this->access_token,
+                "CONTENT_TYPE" => "application/json"
+            ],
+            json_encode([
+                'attendee_email' => $memberless_email,
+                'attendee_first_name' => 'Assigned',
+                'attendee_last_name' => 'Attendee',
+            ])
+        );
+
+        $this->assertResponseStatus(412);
+
+        // nothing changed
+        $row = $db->fetchAssociative(
+            'SELECT Email, MemberID, FirstName FROM SummitAttendee WHERE ID = ?',
+            [$memberless_attendee_id]
+        );
+        $this->assertEquals($memberless_email, $row['Email']);
+        $this->assertNull($row['MemberID']);
+        $this->assertNotEquals('Assigned', $row['FirstName']);
+        $this->assertEquals(
+            $tickets_count,
+            $db->fetchOne('SELECT COUNT(ID) FROM SummitAttendeeTicket WHERE OwnerID = ?', [$memberless_attendee_id])
+        );
+        $this->assertEquals(
+            $attendees_count,
+            $db->fetchOne('SELECT COUNT(ID) FROM SummitAttendee WHERE SummitID = ?', [self::$summit->getId()])
+        );
+        $this->assertEquals(
+            $member2_attendee_email,
+            $db->fetchOne('SELECT Email FROM SummitAttendee WHERE ID = ?', [$member2_attendee->getId()])
+        );
+    }
+
+    public function testAssignAttendeeEmailOfMemberWithAnotherAttendeeVerified()
+    {
+        $this->assignTicketToEmailOfMemberOwningAnotherAttendee(true);
+    }
+
+    public function testAssignAttendeeEmailOfMemberWithAnotherAttendeeNotVerified()
+    {
+        $this->assignTicketToEmailOfMemberOwningAnotherAttendee(false);
+    }
+
     public function testRemoveAttendee()
     {
         $assigned_ticket = $this->testAssignAttendee();