fix(Collaboration): Allow to enforce strict email format on sharees API

Only recommend a email address as sharee if it satisfies the strict format checking.
Meaning before `a@b` was valid, while now with strict checking it is invalid and needs
to be at least `a@b.c`

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

lib/private/Collaboration/Collaborators/MailPlugin.php

@@ -26,6 +26,9 @@
  */
 namespace OC\Collaboration\Collaborators;
 
+use Egulias\EmailValidator\EmailValidator;
+use Egulias\EmailValidator\Validation\NoRFCWarningsValidation;
+use Egulias\EmailValidator\Validation\RFCValidation;
 use OC\KnownUser\KnownUserService;
 use OCP\Collaboration\Collaborators\ISearchPlugin;
 use OCP\Collaboration\Collaborators\ISearchResult;
@@ -251,7 +254,15 @@ public function search($search, $limit, $offset, ISearchResult $searchResult): b
 			$userResults['wide'] = array_slice($userResults['wide'], $offset, $limit);
 		}
 
-		if (!$searchResult->hasExactIdMatch($emailType) && $this->mailer->validateMailAddress($search)) {
+		if ($search && !$searchResult->hasExactIdMatch($emailType)) {
+			$strictMailCheck = $this->config->getAppValue('core', 'shareapi_enforce_strict_email', 'yes') === 'yes';
+			$validator = new EmailValidator();
+			$validation = match ($strictMailCheck) {
+				false => new RFCValidation(),
+				true => new NoRFCWarningsValidation(),
+			};
+
+			if ($validator->isValid($search, $validation))
 			$result['exact'][] = [
 				'label' => $search,
 				'uuid' => $search,