When you submit an e-mail with multiple e-mail
addresses and it contains one or more invalid e-mail
adresses, the e-mail is completely rejected for all e-
mail addresses, and you get an error message that only
tells you that there is something wrong with the
address line. You don't know what the problem is,
that it is in fact a bad e-mail address, much less
know which e-mail address is invalid. This is the
only mail server I've experienced that works like
this. Every other e-mail server sends out the e-mail
to the valid e-mail addresses, and returns e-mails to
the sender detailing the specific invalid e-mail
addresses.