What does it mean connect to aspmx.l.google.com:25: Network is unreachable

postfix

I have server with RHEL 6 and postfix (postfix-2.6.6-2.2.el6), When I try to send email to Google I'm getting this in /var/logmaillog:

postfix/smtp[13414]: 6F4DC10406E7: to=<XXX@englishonlineuniversity.com>, relay=none, delay=0.16, delays=0.02/0/0.14/0, dsn=4.4.1, status=deferred (connect to aspmx.l.google.com[2a00:1450:4013:c01::1b]:25: Network is unreachable)

This error occurs only on this domain (englishonlineuniversity.com).

What does it mean connect to aspmx.l.google.com:25: Network is unreachable?

Best Answer

This means your MTA is trying to connect to the Google SMTP via IPv6 (2a00:1450:4013:c01::1b). This doesn't work as your network probably doesn't support IPv6.

To get rid of the error message, you can configure Postfix not to use IPv6 by editing your /etc/postfix/main.cf with this directive:

inet_protocols = ipv4

Afterwards you'll have to restart postfix:

/etc/init.d/postfix restart
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