how to prevent fake email to enter my domain?

[Michael Masse]

>>> On 1/26/2007 at 4:04 AM, in message
<Pine.LNX.4.64.0701262000570.5146 at ebfjryy.nhfvpf.arg>, Res
<res at ausics.net>
wrote:
> You should use a helo check, if you use sendmail use the
block_bad_helo 
> hack for 8.13.x,   8.14.x will have this as a feature, along with
require 
> rdns.

The Block_bad_helo hack works excellent, except there are a few
legitimate senders out there with badly configured servers that send
things like localhost during helo, so you have no choice but to
whitelist some of these senders.    Sendmail-speak is not the easiest
thing to decipher, so make sure you know how to whitelist bad helos
before implementing it.

Mike