Add validation for sender email address

changelog/unreleased/36505

@@ -0,0 +1,5 @@
+Bugfix: enhance validation for sender e-mail address for e-mail notifications
+
+In case an user wanted to use the e-mail notification mechanism in order to notify other users when creating public links as well as internal shares, an error was triggered if the e-mail address for this user was not set. The behavior has now been fixed.  
+
+https://github.com/owncloud/core/pull/36505

lib/private/Share/MailNotifications.php

@@ -183,6 +183,10 @@ public function sendInternalShareMail($sender, $node, $shareType, $recipientList
 				'internal',
 				$recipientL10N
 			);
+			$replyTo = $sender->getEMailAddress();
+			if (empty($replyTo)) {
+				$replyTo = Util::getDefaultEmailAddress('sharing-noreply');
+			}
 
 			// send it out now
 			try {
@@ -192,7 +196,7 @@ public function sendInternalShareMail($sender, $node, $shareType, $recipientList
 				$message->setHtmlBody($htmlBody);
 				$message->setPlainBody($textBody);
 				$message->setFrom($this->getFrom($this->l, $filter->getSenderDisplayName()));
-				$message->setReplyTo([$sender->getEMailAddress()]);
+				$message->setReplyTo([$replyTo]);
 
 				$this->mailer->send($message);
 			} catch (\Exception $e) {
@@ -264,6 +268,9 @@ public function sendLinkShareMail($sender, $recipients, $link, $personalNote = n
 		);
 		$from = $this->getFrom($l10n, $filter->getSenderDisplayName());
 		$replyTo = $sender->getEMailAddress();
+		if (empty($replyTo)) {
+			$replyTo = Util::getDefaultEmailAddress('sharing-noreply');
+		}
 
 		$event = new GenericEvent(null, ['link' => $link, 'to' => $recipientsAsString]);
 		$this->eventDispatcher->dispatch('share.sendmail', $event);