major.io words of wisdom from a systems engineer

Fixing Invalid HELO’s

If your server is spewing an invalid HELO, you could be blacklisted pretty quickly. The Spamhaus SBL-XBL list and CBL list work together to find servers announcing themselves improperly.

The common reasons why mail servers are blocked for bad HELO’s are:

  • Server is announcing itself as “localhost”.
  • Server is announcing itself as an IP address.
  • Server is announcing itself as a hostname that does not exist.

Are you unsure what your server’s announcing itself as? Try these:

  • Send an e-mail to [email protected] You will get an immediate response with exactly what your HELO contains.
  • Telnet to port 25 on your mailserver. Run telnet mail.yourdomain.com 25 and wait a few seconds. Your server’s HELO message should appear.

So your server is announcing itself as the wrong thing? Well, fix it!

Managing HELO with QMail

If /var/qmail/control/me exists, edit it so that it matches your reverse DNS record for your server’s primary IP address. If the file doesn’t exist, you can create the file and add the correct hostname to it, or adjust your hostname on your operating system. Try running hostname mail.yourdomain.com to fix things immediately, and edit the proper configuration files to correct your hostname at boot time.

Managing HELO with Postfix

The default value for Postfix’s HELO is the value of $myhostname. If that variable is defined in the main.cf, adjust it so that it matches the reverse DNS record of your server. If it isn’t defined in main.cf, then adjust the hostname on your operating system. Try running hostname mail.yourdomain.com to fix things immediately, and edit the proper configuration files to correct your hostname at boot time. Should neither of those methods suffice on your server, simply adjust the smtp_helo_name variable to match the reverse DNS record of your server. For example:

smtp_helo_name = mail.yourdomain.com

Managing HELO with Sendmail

Adjust the hostname on your operating system. Try running hostname mail.yourdomain.com to fix things immediately, and edit the proper configuration files to correct your hostname at boot time.