Block External Relay to Local Domains 1

[dthompson82]

Hi everyone,

We are having some issues with users receiving emails from fake internal email addresses, from external servers.

What I want to do is stop external servers from being able to send to internal users, when they attempt to use an email address that is not a valid recipient or alias.

Currently the following scenario will work:
External server at 123.123.123.123 connects to our mail server and sends from fakeuser@our.domain.com.au to realuser@ourdomain.com.au.

If there a way to make PostFix check the FROM user when the specified domain is one of our locally defined domains?

Cheers.

 

[arbenin]

I would try to filter this out on HELO phase -- require FQDN and reject everybody who wants to look like me, e.g.

smtpd_helo_restrictions =
  permit_mynetworks
  reject_non_fqdn_hostname
  reject_invalid_hostname
  check_helo_access hash:/etc/postfix/helo_access
  permit

File /etc/postfix/helo_access

our.domain.com.au REJECT
localhost REJECT
MY.IP.AD.RS REJECT

By the way, this is a good article on how to configure Postfix to filter out spam.

http://www.freesoftwaremagazine.com/articles/focus_spam_postfix

Cheers,

http://arbenin.reachby.com