"IPv6 support is disabled" warnings

To disable the messsage, go to /etc/postfix/main.cf and change from:

inet_protocols = all

to:

inet_protocols = ipv4

This will only use ipv4 and the warning message will go away.

You will have to issue a stop and start for postfix to register the change. A simple reload will yield:

mail postfix/master[8330]: reload -- version 2.9.6, configuration /etc/postfix mail postfix/master[8330]: warning: ignoring inet_protocols parameter value change mail postfix/master[8330]: warning: old value: "all", new value: "ipv4" mail postfix/master[8330]: warning: to change inet_protocols, stop and start Postfix

You don't have IPv6 configured in your OS's network stack, but your mailer (presumably postfix) is configured to use IPv6. Since there is no IPv6 for your mailer to use, it's warning you that it's only going to use IPv4. From the postfix readme:

if you see error messages like the following, then you're running Linux and need to turn on IPv6 in the kernel: see http://www.ipv6.org/ for hints and tips. Unlike other systems, Linux does not have a combined stack for IPv4 and IPv6, and IPv6 protocol support is not loaded by default.

postconf: warning: inet_protocols: IPv6 support is disabled: Address family not supported by protocol
postconf: warning: inet_protocols: configuring for IPv4 support only