Sophos SG230 UTM - Firmware 9.707-5
Was getting Remote Server returned '554 5.0.0 < #5.0.0>' when sending emails from on premise Exchange 2016 server.
To one email domain only. All emails inbound or outbound were sitting in the SMTP spool in the waiting condition.
The errors when retrying says connection refused - totally unrelated to the Country Blocking.
Turns out the email address was a client in Turkey. Turkey was blocked in the Country Block List in Sophos.
Apparently Sophos does not show that error to the user or the IT department.
After unblocking Turkey emails flow normally to this domain.
the full message behind returned '554 5.0.0 < #5.0.0>'" would be useful.Seems your client check the existence from your mailserver behind your MX record ....I think this test is made via SMTP ... i exclude SMTP from Country-blocking (via CB exceptions)
Sophos Solution Partner since 2003 If a post solves your question, click the 'Verify Answer' link at this post.
Not sure where CB exceptions are. That was the issue I am not getting any more information from the rejection. The SMTP log just shows connection refused, leading me down a rabbit hole looking for issues. No reference to the fact that Sophos was actually blocking the traffic due to the Country Blocking. Once I took Turkey off the block list mail instantly started flowing. Point of my post is Sophos should of tagged the emails being blocked with why they were stuck in the queue waiting to retry.
CB = Country Block