A better solution is to check the ip and see if it is an MX record for
the domain the mail purports to be from.
[de-lurk]
Perhaps, but do recall that there are systems out there which have certain servers listed in the MX records for receiving mail, and different servers for sending mail that aren't listed in the MX records.
You can't please everybody, I guess.
Apologies to Daniel, as he would receive two copies of this message.