[tlug] Sendmail not behaving itself

["Scott McLennan" <scottmclennan@example.com>]

Im having with problems with my sendmail setup.
Im using linux 7.1 and have dns set up and mx
set up fine as far as I can see. The trouble is that
yesterday I sent an email from outside of the network
and it didnt come through. It came back with 
'Bad Format Error'. I was really surprised and kept
sending messages from other places such as yahoo
etc., After about 5 messages, my messages came
through but I have no idea what the problem is.
I could send to 
root@example.com
scotty@example.com
and for those users for the following domains.
www.official-tpcmember.com
www.snowball.meguro.tokyo.jp
www.scottmclennan.com

but the mail didnt get through.
It was really annoying and upsetting after all the work Id put in..
How can I debug this so that I can make my mail server a cement
fortress which will will never buckle under any load at all... 

Scott