ARGH!!! invalid sender when checking wp-mail.php

i have been using WP 1.5 and the post via mail function just fine up until today! my cron jobs work to check wp-mail.php and i have several WP 1.5 accts running nicely.

all of a sudden, one of my accts is acting funky and i get this error:

Invalid sender: <[email protected]> !

Not adding email!

SO, i am confused what happened?? i checked the email acct on my own to discover everything in the headers is the same as before. i am the only admin on the account so nobody could have changed anything.

here are my questions:
(1) does WP look at other headers in the email to validate the email address? if so, what can i do to go around this?

(2) what could possibly be screwing this up all of a sudden. like i said, this was working perfectly and now all of a sudden is busted. i don’t get it. quadruple checked everything and all things are typed perfectly. this appears to be a case where some other header is messing things up and i can’t figure it out.

your help tracking this down is greatly appreciated it.