Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
New Member

Callback setup failed while verifying

Hi there!

It's the second time I have this kind of problem with a customer. The message is:

5.1.0 - Unknown address error 550-'Callback setup failed while verifying <\n(result of an earlier callout reused).\nThe initial connection, or a HELO or MAIL FROM:<> command was\nrejected. Refusing MAIL FROM:<> does not help fight spam, disregards\nRFC requirements, and stops you from receiving standard bounce\nmessages. This host does not accept mail from domains whose servers\nrefuse bounces.\nUser Not Found!' (delivery attempts: 0)

Some one heard about it ?

Regards !


Re: Callback setup failed while verifying


Yes this sounds a lot like you where using the bounce verification feature. The reply to address is changes, where bounces should get delivered to and which you would accept. However the other MTA is looking at the mail-from which is not accepted since it does not have a valid bounce tag.

You would need to configure in an Mail flow policy that is catching there sending IP address ( having the right sendergroup attached to it - I would create a new one with there IP address ) and that does not have the checkbox checked for bounce verification. (accept untagged bounces =Yes)

Best Regards,


CreatePlease login to create content