diff --git a/lib/Service/MailTransmission.php b/lib/Service/MailTransmission.php
index 2ce080a17a..c06211789f 100644
--- a/lib/Service/MailTransmission.php
+++ b/lib/Service/MailTransmission.php
@@ -15,6 +15,7 @@
 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;
@@ -151,6 +152,14 @@ public function sendMessage(Account $account, LocalMessage $localMessage): void
 			}
 			$localMessage->setStatus(LocalMessage::STATUS_ERROR);
 			return;
+		} finally {
+			if ($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(