Yah it's a joke, so no religion flamebaits.
Some stuff I feel like pointing out:
-A christian(probably priest), an unknown person(who I think is a Jew because it's one of the three most known religions, and Osama had sent God the same message, titled "LET ALL UNBELIEVERS PERISH". Possibly a poke at people thinking that their gods were different but in fact one same god for every religion?
-Note the 'rdawkins@oxford.edu' who obviously is Dawkins mailing God that he is non-existant.
-Zeus asking to have lunch together. Since Zeus is a god as well.
-'mel@oldtimereligion.org' asking God about apologising. Mel Gibson asking if he should apologise to Jews?
-'jc@kingdom.net' obviously is Jesus telling God to stop forwarding him lottery requests.
Loads more fun but I'm not gonna spoil it all for ya, have fun laughing/getting offended.