More clarity is required, I don't know what their email is and I don't know what yours is or the printers.
So.
The email address the alerts are going to, is it the same one you are trying to mail to from the UI?
How about if the IT team places their email address as the from address, what happens then?
Is there any sort of authentication done at the machine?
If your IT can do a wireshark trace of the failed email transaction Xerox 2nd level can analyze it and tell you exactly what is happening. Obviously you don't want to post a wireshark trace on this forum so you would need to initiate the call on your end.