[BlueOnyx:26338] Re: Backscatter / user not found bounce

[Ken Hohhof]

Wait, that's an SMTP error code, is your server rejecting the email during the SMTP session, or sending a bounce email to the (probably spoofed) sender?  It should be doing the first one.  The second one is bad, I think the term is asynchronous bounce?

Are you using some sort of MX relay to do email filtering, so that by the time your BO server rejects the connection for no valid recipients, the outboard solution has already terminated its SMTP session and sends a bounce email?  Otherwise, I don't see how an SMTP reject would be backscatter.

-----Original Message-----
From: Blueonyx <blueonyx-bounces at mail.blueonyx.it> On Behalf Of Colin Jack via Blueonyx
Sent: Sunday, July 2, 2023 12:18 PM
To: Blueonyx at mail.blueonyx.it
Subject: [BlueOnyx:26336] Backscatter / user not found bounce

We are having issues with spammers sending thousands of emails to non-existent users on our hosted domains and our BX server then bouncing them as "554 5.5.1 Error: no valid recipients" and our IP consequently getting blacklisted for backscatter. 

Microsoft hate us now – Hotmail etc. and block all email from our subnet! :-/

5210R

Is there any practical way to stop “no valid recipient” email being sent out from the server?

Thanks

Colin


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