relay=none, delay=508, delays=508/0.02/0.02/0, dsn=4.4.1, status=deferred (connect to aspmx2.googlemail.com[IPv6 Address]:25: Network is unreachable)

If anyone is getting the above message or similar it’s being caused by Gmail now accepting mail over IPv6 and your server is failing to connect to their server for some reason to fix this in postfix I simply forced it to use IPv4 until I have the time to spend setting up IPv6 mail.

In postfix open:

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/etc/postfix/main.cf

Set Postfix IPv4 Only

Find the line starting with “inet_protocols” and make sure it reads:

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inet_protocols=ipv4

(On CentOS the default was inet_protocols=all)

Restart  or reload Postfix.

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/etc/init.d/postfix reload

You might want to flush the mail queue in Postfix or just wait and mail will start to send, note you will probably have backed up email.

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postfix -f