Seeing many bad emails with bad DNS entries.

For example

swallowwire.sa.com

It has an A record but the MX record points to protection.outlook.com 
which is an invalid host name, so Microsoft does not give back any ip 
addresses for this host.

I am running a smart host that forwards to my mail server.  My personal 
mail server uses Clamav with the securite extra spam definations.  This 
is causing rejects from my personal mail server and it bounces the 
email.  Now my smart host is trying to send back the NDR to the sender.

This is where things go sideways.  You have an MX record, but that does 
not resolve to a valid host ip address. Now the NDR is stuck at the 
smart host.  I have some scripts that monitor the number of queued 
messages and I get alerts because of the pileup in the message queue on 
the smart host.

In addition there is a minor bug in Surgemail, when I deleted multiple 
messages from the webadmin interface, Surgemail does not properly clear 
the unsent yet count or the unsent yet-q count on the Status page.  
Which is what I am monitoring to determine if there are too many 
messages stuck in the queue.

Where do I go from here to stop this fine mess the spammers put me in?

Lyle Giese