Google and other email services sometimes block messages sent from an IPv6 address. Sending mail over IPv4 instead is sometimes an easy solution. If you are using Postfix, you can force your outbound emails to be sent over IPv4 by doing the following:

  • Open /etc/postfix/main.cf with a text editor
  • Find the line inet_protocols = all
  • Replace all with ipv4
  • Restart postfix
You should also make sure you have RDNS set up for any IP that you want to send email from. Please see this article for help with RDNS.
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