[Exim] Server response to error codes

Hey,

Does anyone have a source of information on various mail servers and
their response to error codes?

Recently I implemented greylisting on my server named Mailscan (Exim
4.34); but I noticed that our Groupwise 5.5 bounces the outgoing mail to
the greylisting Exim server at 451 after RCPT. This is a test situation
now. I need to know what other mail servers are going to do with a 451.

Any information sources on this?

Thanks,
Craig