Re: I'm a beginner and want to setup Postfix on CentOS.

[Remco Rijnders]

On Mon, Oct 12, 2020 at 02:54:55PM +0000, Jason wrote in 
<1093127483.422330.1602514495...@mail.yahoo.com>:
Thank you for your reply.
How can I sure I'm using IPv4 or IPv6?

You have both on your system. When you telnetted to localhost, it used ipv6 (see
the "Trying ::1..." part). You do not have that listed in your mynetworks
section. Try adding "[::1]/128" to your mynetworks setting and try again.