diff --git a/apps/dav/lib/CalDAV/Schedule/IMipPlugin.php b/apps/dav/lib/CalDAV/Schedule/IMipPlugin.php
index 18d7559f1a702..37eb9b952068c 100644
--- a/apps/dav/lib/CalDAV/Schedule/IMipPlugin.php
+++ b/apps/dav/lib/CalDAV/Schedule/IMipPlugin.php
@@ -147,6 +147,19 @@ public function schedule(Message $iTipMessage) {
 		$oldEvents = $this->getVCalendar();
 
 		$modified = $this->eventComparisonService->findModified($newEvents, $oldEvents);
+		// A newly cancelled occurrence is announced through the separate CANCEL
+		// message; it rides along in the REQUEST only so the attendee's stored copy
+		// stays cancelled and must not produce an invitation email of its own.
+		if (strcasecmp($iTipMessage->method, self::METHOD_REQUEST) === 0 && !empty($modified['new'])) {
+			$modified['new'] = array_values(array_filter(
+				$modified['new'],
+				fn (VEvent $component): bool => !$this->isNewlyCancelledOccurrence($component, $oldEvents),
+			));
+			if (empty($modified['new'])) {
+				$iTipMessage->scheduleStatus = '1.0;We got the message, but it\'s not significant enough to warrant an email';
+				return;
+			}
+		}
 		/** @var VEvent $vEvent */
 		$vEvent = array_pop($modified['new']);
 		/** @var VEvent $oldVevent */
@@ -338,6 +351,33 @@ public function schedule(Message $iTipMessage) {
 		}
 	}
 
+	/**
+	 * Whether this component is an occurrence override that got cancelled in the
+	 * same write that created it - the only case the broker announces through a
+	 * per-instance CANCEL message. Cancelling a previously modified occurrence
+	 * produces no CANCEL message, so that override must keep its REQUEST email.
+	 * Mirrors the broker's instance tracking, which only registers components
+	 * carrying an ATTENDEE.
+	 */
+	private function isNewlyCancelledOccurrence(VEvent $component, ?VCalendar $oldEvents): bool {
+		if (!isset($component->STATUS) || $component->STATUS->getValue() !== 'CANCELLED'
+			|| !isset($component->{'RECURRENCE-ID'})) {
+			return false;
+		}
+		if ($oldEvents === null) {
+			return true;
+		}
+		$recurrenceId = $component->{'RECURRENCE-ID'}->getValue();
+		foreach ($oldEvents->getComponents() as $oldComponent) {
+			if ($oldComponent instanceof VEvent
+				&& isset($oldComponent->ATTENDEE, $oldComponent->{'RECURRENCE-ID'})
+				&& $oldComponent->{'RECURRENCE-ID'}->getValue() === $recurrenceId) {
+				return false;
+			}
+		}
+		return true;
+	}
+
 	/**
 	 * @return ?VCalendar
 	 */
diff --git a/apps/dav/lib/CalDAV/TipBroker.php b/apps/dav/lib/CalDAV/TipBroker.php
index e83111330328b..3816f7fcd5de5 100644
--- a/apps/dav/lib/CalDAV/TipBroker.php
+++ b/apps/dav/lib/CalDAV/TipBroker.php
@@ -262,6 +262,23 @@ protected function allowInvitationForwarding(VEvent $vevent): bool {
 		return true;
 	}
 
+	/**
+	 * parseEventInfo() aggregates STATUS with the last parsed component winning,
+	 * so a kept cancelled override would mark the whole event as cancelled and
+	 * suppress the attendee's replies for the remaining occurrences; judge the
+	 * event status by the master instance instead.
+	 *
+	 * @return array<int,Message>
+	 */
+	#[\Override]
+	protected function parseEventForAttendee(VCalendar $calendar, array $eventInfo, array $oldEventInfo, $attendee) {
+		if (isset($eventInfo['instances']['master'])) {
+			$status = $eventInfo['instances']['master']->STATUS?->getValue();
+			$eventInfo['status'] = $status === null ? null : strtoupper($status);
+		}
+		return parent::parseEventForAttendee($calendar, $eventInfo, $oldEventInfo, $attendee);
+	}
+
 	/**
 	 * This method is used in cases where an event got updated, and we
 	 * potentially need to send emails to attendees to let them know of updates
@@ -319,13 +336,11 @@ protected function parseEventForOrganizer(VCalendar $calendar, array $eventInfo,
 			}
 			return $messages;
 		}
-		// detect if a new cancelled instance was created
-		$cancelledNewInstances = [];
+		// detect if a new cancelled instance was created and send a CANCEL for it
 		if (isset($oldEventInfo['instances'])) {
 			$instancesDelta = array_diff_key($eventInfo['instances'], $oldEventInfo['instances']);
 			foreach ($instancesDelta as $id => $instance) {
 				if ($instance->STATUS?->getValue() === 'CANCELLED') {
-					$cancelledNewInstances[] = $id;
 					foreach ($eventInfo['attendees'] as $attendee) {
 						$messages[] = $this->generateMessage(
 							[$id => $instance], $organizerHref, $organizerName, $attendee, $objectId, $objectType, $objectSequence, 'CANCEL', $template
@@ -366,10 +381,10 @@ protected function parseEventForOrganizer(VCalendar $calendar, array $eventInfo,
 			// otherwise any created or modified instances will be sent as REQUEST
 			$instances = array_intersect_key($eventInfo['instances'], array_flip(array_keys($eventInfo['attendees'][$attendee]['instances'])));
 
-			// Remove already-cancelled new instances from REQUEST
-			if (!empty($cancelledNewInstances)) {
-				$instances = array_diff_key($instances, array_flip($cancelledNewInstances));
-			}
+			// Keep newly cancelled instances IN the REQUEST. processMessageRequest replaces all
+			// components of the attendee's stored object with the ones from the message, so a
+			// REQUEST that omitted the cancelled instance would drop the CANCELLED override that
+			// the accompanying CANCEL added and the occurrence would reappear as a normal event.
 
 			// Skip if no instances left to send
 			if (empty($instances)) {
diff --git a/apps/dav/tests/unit/CalDAV/Schedule/IMipPluginTest.php b/apps/dav/tests/unit/CalDAV/Schedule/IMipPluginTest.php
index 048dcd13b67e3..1ab44d90cc835 100644
--- a/apps/dav/tests/unit/CalDAV/Schedule/IMipPluginTest.php
+++ b/apps/dav/tests/unit/CalDAV/Schedule/IMipPluginTest.php
@@ -1237,4 +1237,271 @@ public function testExternalAttendeesDisabledForSystemUser(): void {
 		$this->plugin->schedule($message);
 		$this->assertEquals('1.1', $message->getScheduleStatus());
 	}
+
+	public function testRequestWithOnlyCancelledOccurrenceSendsNoEmail(): void {
+		$message = new Message();
+		$message->method = 'REQUEST';
+		$newVCalendar = new VCalendar();
+		$cancelledOverride = new VEvent($newVCalendar, 'one', [
+			'UID' => 'uid-1234',
+			'RECURRENCE-ID' => new \DateTime('2016-01-08 00:00:00'),
+			'SEQUENCE' => 1,
+			'STATUS' => 'CANCELLED',
+			'SUMMARY' => 'Fellowship meeting',
+			'DTSTART' => new \DateTime('2016-01-08 00:00:00'),
+		]);
+		$cancelledOverride->add('ORGANIZER', 'mailto:gandalf@wiz.ard');
+		$cancelledOverride->add('ATTENDEE', 'mailto:' . 'frodo@hobb.it', ['RSVP' => 'TRUE']);
+		$message->message = $newVCalendar;
+		$message->sender = 'mailto:gandalf@wiz.ard';
+		$message->senderName = 'Mr. Wizard';
+		$message->recipient = 'mailto:' . 'frodo@hobb.it';
+		$message->significantChange = true;
+		// stored old copy: the series without the override, so the cancelled
+		// override is newly created in this write
+		$oldVCalendar = new VCalendar();
+		$oldVCalendar->add(new VEvent($oldVCalendar, 'one', [
+			'UID' => 'uid-1234',
+			'SEQUENCE' => 0,
+			'SUMMARY' => 'Fellowship meeting',
+			'DTSTART' => new \DateTime('2016-01-01 00:00:00'),
+		]));
+		$this->plugin->setVCalendar($oldVCalendar);
+
+		$this->service->expects(self::once())
+			->method('getLastOccurrence')
+			->willReturn(1496912700);
+		$this->config->expects(self::once())
+			->method('getValueBool')
+			->with('dav', 'caldav_external_attendees_disabled', false)
+			->willReturn(false);
+		// The REQUEST carries only the cancelled override, kept so the attendee's
+		// stored copy stays cancelled through Sabre's full component replace. The
+		// occurrence cancellation is announced by the accompanying CANCEL message,
+		// so this REQUEST must not additionally send an invitation email.
+		$this->eventComparisonService->expects(self::once())
+			->method('findModified')
+			->willReturn(['new' => [$cancelledOverride], 'old' => []]);
+		$this->service->expects(self::never())
+			->method('getCurrentAttendee');
+		$this->service->expects(self::never())
+			->method('buildBodyData');
+		$this->mailer->expects(self::never())
+			->method('send');
+		// deliberate suppression, not the "significant but nothing changed" anomaly
+		$this->logger->expects(self::never())
+			->method('warning');
+
+		$this->plugin->schedule($message);
+		$this->assertEquals('1.0', $message->getScheduleStatus());
+	}
+
+	public function testRequestForCancelledExistingOccurrenceStillSendsEmail(): void {
+		$message = new Message();
+		$message->method = 'REQUEST';
+		$newVCalendar = new VCalendar();
+		$cancelledOverride = new VEvent($newVCalendar, 'one', [
+			'UID' => 'uid-1234',
+			'RECURRENCE-ID' => new \DateTime('2016-01-08 00:00:00'),
+			'SEQUENCE' => 2,
+			'STATUS' => 'CANCELLED',
+			'SUMMARY' => 'Fellowship meeting',
+			'DTSTART' => new \DateTime('2016-01-08 00:00:00'),
+		]);
+		$cancelledOverride->add('ORGANIZER', 'mailto:gandalf@wiz.ard');
+		$cancelledOverride->add('ATTENDEE', 'mailto:' . 'frodo@hobb.it', ['RSVP' => 'TRUE']);
+		$message->message = $newVCalendar;
+		$message->sender = 'mailto:gandalf@wiz.ard';
+		$message->senderName = 'Mr. Wizard';
+		$message->recipient = 'mailto:' . 'frodo@hobb.it';
+		$message->significantChange = true;
+		// stored old copy already contains a live override for this occurrence:
+		// no CANCEL message is generated for it, this REQUEST is the only notice
+		$oldVCalendar = new VCalendar();
+		$oldVCalendar->add(new VEvent($oldVCalendar, 'one', [
+			'UID' => 'uid-1234',
+			'SEQUENCE' => 0,
+			'SUMMARY' => 'Fellowship meeting',
+			'DTSTART' => new \DateTime('2016-01-01 00:00:00'),
+		]));
+		$oldOverride = new VEvent($oldVCalendar, 'one', [
+			'UID' => 'uid-1234',
+			'RECURRENCE-ID' => new \DateTime('2016-01-08 00:00:00'),
+			'SEQUENCE' => 1,
+			'SUMMARY' => 'Fellowship meeting',
+			'DTSTART' => new \DateTime('2016-01-08 00:00:00'),
+		]);
+		$oldOverride->add('ORGANIZER', 'mailto:gandalf@wiz.ard');
+		$oldOverride->add('ATTENDEE', 'mailto:' . 'frodo@hobb.it', ['RSVP' => 'TRUE']);
+		$oldVCalendar->add($oldOverride);
+		$this->plugin->setVCalendar($oldVCalendar);
+		$data = [
+			'invitee_name' => 'Mr. Wizard',
+			'meeting_title' => 'Fellowship meeting',
+			'attendee_name' => 'frodo@hobb.it',
+		];
+		$attendees = $cancelledOverride->select('ATTENDEE');
+		$atnd = '';
+		foreach ($attendees as $attendee) {
+			if (strcasecmp($attendee->getValue(), $message->recipient) === 0) {
+				$atnd = $attendee;
+			}
+		}
+		$this->service->expects(self::once())
+			->method('getLastOccurrence')
+			->willReturn(1496912700);
+		$this->config->expects(self::exactly(2))
+			->method('getValueBool')
+			->willReturnMap([
+				['dav', 'caldav_external_attendees_disabled', false, false],
+				['core', 'mail_providers_enabled', true, false],
+			]);
+		$this->eventComparisonService->expects(self::once())
+			->method('findModified')
+			->willReturn(['new' => [$cancelledOverride], 'old' => [$oldOverride]]);
+		$this->service->expects(self::once())
+			->method('getCurrentAttendee')
+			->with($message)
+			->willReturn($atnd);
+		$this->service->expects(self::once())
+			->method('isRoomOrResource')
+			->with($atnd)
+			->willReturn(false);
+		$this->service->expects(self::once())
+			->method('isCircle')
+			->with($atnd)
+			->willReturn(false);
+		$this->service->expects(self::once())
+			->method('buildBodyData')
+			->with($cancelledOverride, $oldOverride)
+			->willReturn($data);
+		$this->service->expects(self::once())
+			->method('getFrom');
+		$this->service->expects(self::once())
+			->method('addSubjectAndHeading')
+			->with($this->emailTemplate, 'request', 'Mr. Wizard', 'Fellowship meeting', true);
+		$this->service->expects(self::once())
+			->method('addBulletList')
+			->with($this->emailTemplate, $cancelledOverride, $data);
+		$this->service->expects(self::once())
+			->method('getAttendeeRsvpOrReqForParticipant')
+			->willReturn(false);
+		$this->mailer->expects(self::once())
+			->method('send')
+			->willReturn([]);
+		$this->plugin->schedule($message);
+		$this->assertEquals('1.1', $message->getScheduleStatus());
+	}
+
+	public function testRequestKeepsChangeWhenCancelledOccurrenceIsAlsoPresent(): void {
+		$message = new Message();
+		$message->method = 'REQUEST';
+		$newVCalendar = new VCalendar();
+		$newVevent = new VEvent($newVCalendar, 'one', [
+			'UID' => 'uid-1234',
+			'SEQUENCE' => 1,
+			'SUMMARY' => 'Fellowship meeting without (!) Boromir',
+			'DTSTART' => new \DateTime('2016-01-01 00:00:00'),
+		]);
+		$newVevent->add('ORGANIZER', 'mailto:gandalf@wiz.ard');
+		$newVevent->add('ATTENDEE', 'mailto:' . 'frodo@hobb.it', ['RSVP' => 'TRUE', 'CN' => 'Frodo']);
+		$cancelledOverride = new VEvent($newVCalendar, 'one', [
+			'UID' => 'uid-1234',
+			'RECURRENCE-ID' => new \DateTime('2016-01-08 00:00:00'),
+			'SEQUENCE' => 1,
+			'STATUS' => 'CANCELLED',
+			'SUMMARY' => 'Fellowship meeting without (!) Boromir',
+			'DTSTART' => new \DateTime('2016-01-08 00:00:00'),
+		]);
+		$cancelledOverride->add('ORGANIZER', 'mailto:gandalf@wiz.ard');
+		$cancelledOverride->add('ATTENDEE', 'mailto:' . 'frodo@hobb.it', ['RSVP' => 'TRUE']);
+		$message->message = $newVCalendar;
+		$message->sender = 'mailto:gandalf@wiz.ard';
+		$message->senderName = 'Mr. Wizard';
+		$message->recipient = 'mailto:' . 'frodo@hobb.it';
+		$message->significantChange = true;
+		$oldVCalendar = new VCalendar();
+		$oldVEvent = new VEvent($oldVCalendar, 'one', [
+			'UID' => 'uid-1234',
+			'SEQUENCE' => 0,
+			'SUMMARY' => 'Fellowship meeting',
+			'DTSTART' => new \DateTime('2016-01-01 00:00:00'),
+		]);
+		$oldVEvent->add('ORGANIZER', 'mailto:gandalf@wiz.ard');
+		$oldVEvent->add('ATTENDEE', 'mailto:' . 'frodo@hobb.it', ['RSVP' => 'TRUE', 'CN' => 'Frodo']);
+		$oldVCalendar->add($oldVEvent);
+		$data = [
+			'invitee_name' => 'Mr. Wizard',
+			'meeting_title' => 'Fellowship meeting without (!) Boromir',
+			'attendee_name' => 'frodo@hobb.it',
+		];
+		$attendees = $newVevent->select('ATTENDEE');
+		$atnd = '';
+		foreach ($attendees as $attendee) {
+			if (strcasecmp($attendee->getValue(), $message->recipient) === 0) {
+				$atnd = $attendee;
+			}
+		}
+		$this->plugin->setVCalendar($oldVCalendar);
+		$this->service->expects(self::once())
+			->method('getLastOccurrence')
+			->willReturn(1496912700);
+		$this->config->expects(self::exactly(2))
+			->method('getValueBool')
+			->willReturnMap([
+				['dav', 'caldav_external_attendees_disabled', false, false],
+				['core', 'mail_providers_enabled', true, false],
+			]);
+		// The cancelled override rides along in the REQUEST but must not become the
+		// event the email describes: it is dropped, leaving the real change.
+		$this->eventComparisonService->expects(self::once())
+			->method('findModified')
+			->willReturn(['new' => [$newVevent, $cancelledOverride], 'old' => [$oldVEvent]]);
+		$this->service->expects(self::once())
+			->method('getCurrentAttendee')
+			->with($message)
+			->willReturn($atnd);
+		$this->service->expects(self::once())
+			->method('isRoomOrResource')
+			->with($atnd)
+			->willReturn(false);
+		$this->service->expects(self::once())
+			->method('isCircle')
+			->with($atnd)
+			->willReturn(false);
+		$this->service->expects(self::once())
+			->method('buildBodyData')
+			->with($newVevent, $oldVEvent)
+			->willReturn($data);
+		$this->service->expects(self::once())
+			->method('getFrom');
+		$this->service->expects(self::once())
+			->method('addSubjectAndHeading')
+			->with($this->emailTemplate, 'request', 'Mr. Wizard', 'Fellowship meeting without (!) Boromir', true);
+		$this->service->expects(self::once())
+			->method('addBulletList')
+			->with($this->emailTemplate, $newVevent, $data);
+		$this->service->expects(self::once())
+			->method('getAttendeeRsvpOrReqForParticipant')
+			->willReturn(true);
+		$this->config->expects(self::once())
+			->method('getValueString')
+			->with('dav', 'invitation_link_recipients', 'yes')
+			->willReturn('yes');
+		$this->service->expects(self::once())
+			->method('createInvitationToken')
+			->with($message, $newVevent, 1496912700)
+			->willReturn('token');
+		$this->service->expects(self::once())
+			->method('addResponseButtons')
+			->with($this->emailTemplate, 'token');
+		$this->service->expects(self::once())
+			->method('addMoreOptionsButton')
+			->with($this->emailTemplate, 'token');
+		$this->mailer->expects(self::once())
+			->method('send')
+			->willReturn([]);
+		$this->plugin->schedule($message);
+		$this->assertEquals('1.1', $message->getScheduleStatus());
+	}
 }
diff --git a/apps/dav/tests/unit/CalDAV/TipBrokerTest.php b/apps/dav/tests/unit/CalDAV/TipBrokerTest.php
index 0af957823787b..2ed59bc55136e 100644
--- a/apps/dav/tests/unit/CalDAV/TipBrokerTest.php
+++ b/apps/dav/tests/unit/CalDAV/TipBrokerTest.php
@@ -303,7 +303,37 @@ public function testParseEventForOrganizerCreatedInstanceCancelled(): void {
 		$this->assertEquals($mutatedCalendar->VEVENT[1]->ATTENDEE[0]->getValue(), $messages[0]->recipient);
 		$this->assertCount(1, $messages[0]->message->VEVENT);
 		$this->assertEquals('20240715T080000', $messages[0]->message->VEVENT->{'RECURRENCE-ID'}->getValue());
+		// the REQUEST keeps the cancelled instance, otherwise processMessageRequest (which replaces
+		// all components) would drop the CANCELLED override on the attendee's copy (issue #6655)
+		$this->assertEquals('REQUEST', $messages[1]->method);
+		$this->assertCount(2, $messages[1]->message->VEVENT);
+		$this->assertEquals('20240715T080000', $messages[1]->message->VEVENT[1]->{'RECURRENCE-ID'}->getValue());
+		$this->assertEquals('CANCELLED', $messages[1]->message->VEVENT[1]->STATUS->getValue());
+
+	}
 
+	/**
+	 * Tests attendee responding to the remaining occurrences while their copy
+	 * carries a cancelled single instance
+	 */
+	public function testParseEventForAttendeeReplyWithCancelledInstance(): void {
+		// attendee copy: recurring event plus a cancelled single instance
+		$originalCalendar = clone $this->vCalendar2a;
+		$cancelledInstance = clone $originalCalendar->VEVENT;
+		$cancelledInstance->add('RECURRENCE-ID', '20240715T080000', ['TZID' => 'America/Toronto']);
+		$cancelledInstance->STATUS->setValue('CANCELLED');
+		$originalCalendar->add($cancelledInstance);
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		// attendee accepts the series
+		$mutatedCalendar = clone $originalCalendar;
+		$mutatedCalendar->VEVENT->ATTENDEE['PARTSTAT'] = 'ACCEPTED';
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation - the cancelled instance must not mute the reply
+		$messages = $this->invokePrivate($this->broker, 'parseEventForAttendee', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo, 'mailto:attendee1@example.org']);
+		$this->assertCount(1, $messages);
+		$this->assertEquals('REPLY', $messages[0]->method);
+		$this->assertEquals($mutatedCalendar->VEVENT->ATTENDEE->getValue(), $messages[0]->sender);
+		$this->assertEquals($mutatedCalendar->VEVENT->ORGANIZER->getValue(), $messages[0]->recipient);
 	}
 
 	/**