* The first new parameter is called inet_protocols. This specifies
what
protocols Postfix will use when it makes or accepts network
connections,
and also controls what DNS lookups Postfix will use when it
makes network
connections.
/usr/local/etc/postfix/main.cf:
# You must stop/start Postfix after changing this
parameter.
inet_protocols = ipv4 (DEFAULT: enable IPv4 only)
inet_protocols = all (enable IPv4, and IPv6 if
supported)
inet_protocols = ipv4, ipv6 (enable both IPv4 and IPv6)
inet_protocols = ipv6 (enable IPv6 only)
By default, Postfix uses IPv4 only, because most systems aren't
attached to
an IPv6 network.
o On systems with combined IPv4/IPv6 stacks, attempts to
deliver mail via
IPv6 would always fail with "network unreachable", and those
attempts
would only slow down Postfix.
o Linux kernels don't even load IPv6 protocol support by
default. Any
attempt to use it would fail immediately.
Note 1: you must stop and start Postfix after changing the
inet_protocols
configuration parameter.
Note 2: 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
Note 3: on older Linux and Solaris systems, the setting
"inet_protocols =
ipv6" will not prevent Postfix from accepting IPv4 connections.
Postfix
will present the client IP addresses in IPv6 format, though. In
all other
cases, Postfix always presents IPv4 client IP addresses in the
traditional
dotted quad IPv4 format.