Outgoing connections on port 25 / 587 / 143 blocked over IPv6?

Posted on September 13, 2014

I just moved my servers, including my mailserver to the new ams3 region because of ipv6. i configured postfix to use ipv6 and i recieved my first email over ipv6 without a problem.

But when i try to send mail over ipv6 to other mailserver that support ipv6 like gmail.com the connection times out.

I then used netcat to test it and found that three mail relevant ports seem to be blocked for outgoing connections. SSH works fine.

nc -vz [ipv6-address] 25
nc: connect to [ipv6-address] port 25 (tcp) failed: Connection timed out
nc -vz [ipv6-address] 587
nc: connect to [ipv6-address] port 587 (tcp) failed: Connection timed out
nc -vz [ipv6-address] 143
nc: connect to [ipv6-address] port 143 (tcp) failed: Connection timed out

nc -vz [ipv6-address] 22
Connection to [ipv6-address] 22 port [tcp/ssh] succeeded

Are these ports really blocked? If yes, why?

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Henrik Steffensen

July 17, 2017

You can give priority to IPv4 addresses over IPv6 so that you can continue to send out email without disabling IPv6. You would do that by editing the Droplet’s /etc/gai.conf file and removing the comment (#) from the following line:

Default Configuration: #precedence ::ffff:0:0/96 100

Configuration with Priority to IPv4: precedence ::ffff:0:0/96 100