diff --git a/apps/dav/lib/CalDAV/Schedule/IMipPlugin.php b/apps/dav/lib/CalDAV/Schedule/IMipPlugin.php
index dcac8db2bbd88..4d771f0f7f8cf 100644
--- a/apps/dav/lib/CalDAV/Schedule/IMipPlugin.php
+++ b/apps/dav/lib/CalDAV/Schedule/IMipPlugin.php
@@ -132,8 +132,16 @@ public function beforeWriteContent($uri, INode $node, $data, $modified): void {
 	 * @return void
 	 */
 	public function schedule(Message $iTipMessage) {
-		// Not sending any emails if the system considers the update
-		// insignificant.
+
+		// do not send imip messages if external system already did
+		/** @psalm-suppress UndefinedPropertyFetch */
+		if ($iTipMessage->message?->VEVENT?->{'X-NC-DISABLE-SCHEDULING'}?->getValue() === 'true') {
+			if (!$iTipMessage->scheduleStatus) {
+				$iTipMessage->scheduleStatus = '1.0;We got the message, but iMip messages are disabled for this event';
+			}
+			return;
+		}
+		// Not sending any emails if the system considers the update insignificant
 		if (!$iTipMessage->significantChange) {
 			if (!$iTipMessage->scheduleStatus) {
 				$iTipMessage->scheduleStatus = '1.0;We got the message, but it\'s not significant enough to warrant an email';
diff --git a/apps/dav/tests/unit/CalDAV/Schedule/IMipPluginTest.php b/apps/dav/tests/unit/CalDAV/Schedule/IMipPluginTest.php
index de6218bf5f536..7813a7942feaa 100644
--- a/apps/dav/tests/unit/CalDAV/Schedule/IMipPluginTest.php
+++ b/apps/dav/tests/unit/CalDAV/Schedule/IMipPluginTest.php
@@ -783,4 +783,23 @@ public function testNoButtons(): void {
 		$this->plugin->schedule($message);
 		$this->assertEquals('1.1', $message->getScheduleStatus());
 	}
+
+	public function testImipDisabledForEvent(): void {
+		// construct iTip message with event and attendees
+		$calendar = new VCalendar();
+		$calendar->add('VEVENT', ['UID' => 'uid-1234']);
+		$event = $calendar->VEVENT;
+		$event->add('ORGANIZER', 'mailto:gandalf@wiz.ard');
+		$event->add('ATTENDEE', 'mailto:' . 'frodo@hobb.it', ['RSVP' => 'TRUE',  'CN' => 'Frodo']);
+		$event->add('X-NC-DISABLE-SCHEDULING', 'true');
+		$message = new Message();
+		$message->method = 'REQUEST';
+		$message->message = $calendar;
+		$message->sender = 'mailto:gandalf@wiz.ard';
+		$message->senderName = 'Mr. Wizard';
+		$message->recipient = 'mailto:' . 'frodo@hobb.it';
+		
+		$this->plugin->schedule($message);
+		$this->assertEquals('1.0;We got the message, but iMip messages are disabled for this event', $message->scheduleStatus);
+	}
 }