fix: close smtp connection after sending or on error

Unfortunately, `getSMTPObject()` creates a connection if it's not
already established. Ideally, the connection is already established due
to the send command some lines above so we only close it. There is no
way around it because the wrapped SMTP object is private.

Signed-off-by: Richard Steinmetz <[email protected]>

lib/Service/MailTransmission.php

@@ -30,6 +30,7 @@
 use Horde_Imap_Client_Fetch_Query;
 use Horde_Imap_Client_Ids;
 use Horde_Mail_Transport_Null;
+use Horde_Mail_Transport_Smtphorde;
 use Horde_Mime_Exception;
 use Horde_Mime_Headers;
 use Horde_Mime_Headers_Addresses;
@@ -145,6 +146,14 @@ public function sendMessage(Account $account, LocalMessage $localMessage): void
 			$localMessage->setStatus(LocalMessage::STATUS_SMPT_SEND_FAIL);
 			$this->logger->error($e->getMessage(), ['exception' => $e]);
 			return;
+		} finally {
+			if ($transport instanceof Horde_Mail_Transport_Smtphorde) {
+				try {
+					$transport->getSMTPObject()->logout();
+				} catch (\Throwable $e) {
+					// Handle silently as this is a resource usage optimization
+				}
+			}
 		}
 
 		$this->eventDispatcher->dispatchTyped(