Hello,
since June 2017 I only get Mails stuck in the Mailqueue.
I haven't changed anything.
This is a "Log" that shows in the Mailqueue:
Received: from EUR03-AM5-obe.outbound.protection.outlook.com (mail-oln040092070057.outbound.protection.outlook.com [40.92.70.57])
by m0460.contabo.host...