Blocking spammers based on SMTP HELO command

PROBLEM
Spammers are abusing my machine.

ENVIRONMENT

• On-Premise Server + WebMail Installations: Version 6.0 > Current Version

CAUSE
If you are noticing a spammer is abusing your machine which is identifying with a common "HELO" command via SMTP, you can optionally deny all messages which match this rule.

For example a spammer might be identifying to your server with a fake HELO command which is common for all SMTP transactions.

RESOLUTION

1. Edit /usr/local/atmail/mailserver/configure
2. In the ACL
   

   acl_check_rcpt:

3. You can append the new rule below for the HELO check
   

   deny message = HELO not allowed
   condition = ${if eq{$sender_helo_name}{spammer.com}{yes}{no}}

4. Copy the rule for each domain you wish to check.
5. Restart the Atmail services and the new HELO check is live.
   

   # telnet localhost 25
   Trying 127.0.0.1...
   Connected to localhost.localdomain (127.0.0.1).
   Escape character is '^]'.
   220 nexus.local.atmail.com Welcome to the @Mail SMTP Server ( Exim )
   helo spammer.com
   250 nexus.local.atmail.com Hello localhost [127.0.0.1]
   mail from: test@test.com
   250 OK
   rcpt to: test@nexus.atmail.com
   550 HELO not allowed