Blocking emails comning from <> is agains the email RFCs, as mailservers will send you error messages from <>, and you're required to receive them. If you block them several bad things will happen, among them are:
When an email any of your users sends cannot be delivers they'll not find out.
The servers attempting to send you those error messages may (and many, especially from the big email providers do) stop accepting email from you.
Your server will end up on the 'RFC Ignorant' list, which some email servers use as a blocklist.
Why would you not want to accept email from a user with a local-part of
admin? You can do it with a simple addition to exim.conf, but it's a perfectly valid email address and we get lots of emails daily from our servrs, which come from a user named admin.
The current default version of the exim.conf file installed with DirectAdmin is quite goodl land easily manageable through CustomBuild, but my more advanced file can be found at
http://www.nobaloney.net/spamblocker.html
Jeff
