Peter via Postfix-users:
> Is this behavior of inet_interfaces overridden by smtp_bind_address?
> From the way it's worded it looks to me like the inet_interfaces
> setting overrides smtp_bind_address but this isn't clear to me. Can
> that be clarified (one way or the other)?
In the mean time I the text further. It should address that
question.
Wietse
When smtp_bind_address and/or smtp_bind_address6 are not specified,
the inet_interfaces setting may constrain the source IP address for
an outbound SMTP or LMTP connection.
* When inet_interfaces specifies one IPv4 address, and that is
not a loopback address, the Postfix SMTP client uses that as
the source address for outbound IPv4 connections.
* Otherwise, the Postfix SMTP client does not constrain the source
IPv4 address, and connect using a system-chosen source IPv4
address. This includes the cases where inet_interfaces specifies
all, or no IPv4 address, or one IPv4 address that is a loopback
address, or multiple IPv4 addresses.
* The same reasoning as above applies to the IPv6 protocol and
to the Postfix LMTP client. To disable IPv4 or IPv6 support in
the Postfix SMTP and LMTP client, use inet_protocols.
A Postfix SMTP client may fail to reach some remote SMTP servers
when the client source IP address is constrained explicitly with
smtp_bind_address or smtp_bind_address6, or implicitly with
inet_interfaces. This can happen when Postfix runs on a multi-homed
system such as a firewall, the Postfix SMTP source client IP address
is constrained to one specific network interface, and the remote
SMTP server must be reached through a different interface. Setting
smtp_bind_address to 0.0.0.0 avoids the potential problem for IPv4,
and setting smtp_bind_address6 to :: solves the problem for IPv6.
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