How To Fix Email Service Unavailable Delivery Issues with IPv6 on Amazon Linux

Published Date Author: , Posted July 16th, 2021 at 2:30:23pm

PROBLEM: Email delivery to Google was failing with a “Service Unavailable” error:

Note that the network address for the destination is shown as IPv6!

That is the root cause of the issue:
1. Sendmail is sending mail from the IPv6 address instead of the IPv4 address
2. Google rejects IPv6 senders without proper reverse DNS lookup or SPF records


Configure sendmail to use the IPv4 address family and pattern:


EXECUTE: /etc/mail/make

EXECUTE: service sendmail restart

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