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Blocking Spammers Based On SMTP HELO Command

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.

Fail2Ban For Exim SMTP Auth

Fail2Ban is a great utility which can be found via: It checks for the output of various log files, and assigns an action to take, based on the IP address in the log file.This can be handy for introducing lockouts for various services. In this scenario, we will use Fail2Ban to create a lockout time for 3 consecutive failed logins to Exim SMTP Auth, via IP tables.

Hardcoded Return Paths

On some systems behind the Barracuda Firewall, you may find the following error message: 2012-01-26 14:47:20 1RqY6C-00070U-Kb ** R=dnslookup T=remote_smtp: SMTP error from remote mail server after RCPT TO:: host []: 550 Empty envelope senders not allowed

Scan Outgoing Emails For Spam

By default, Exim only checks inbound emails for spam. This is easily fixable, via the following steps:

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