[exim] ipv4 "interface" stm disregarded when on IPv6?

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Author: Tom Preissler
Date:  
To: exim-users
Subject: [exim] ipv4 "interface" stm disregarded when on IPv6?
Hi,

I recently setup SPF/DKIM/DMARC on my mail server, so far quite happy
with it and Exim. I have some commercial domains on my server and these
were using my "private" domain and IP for emailling out. As I didn't
want to get my "private" IP blacklisted - just in case - I setup
domain-specific rules, ie: I duplicated remote_smtp and bound it to the
"commercial" IPv4 and a router decides which transport to use depending on
the sender domain. I also have IPv6 enabled as well, web+email.
So far so good, all working.

I noticed now that I am getting "fails" back from DMARC for SPF on my
commercial domain.

It appears to me that when emailling @gmail.com from my commercial
domain, it *always* goes out via the main IPv6 address. This is kinda
expected, as I am IPv6 enabled and Google, too. But it's kinda
unexpected as I am specifically telling it on the remote_smtp_cc
transport to use a valid, local IPv4 address. This IPv4 address was used
just fine when doing tests when I configured the "multi-domain" setup.

I am aware I could fix this by adding a separate IPv6 address to the
commercial mailer+DNS. Yeah, there are plenty of IPv6 addresses out there.


Is this "wanted" behaviour? Does IPv6 takes precedence over a specific
"interface" statement? I have to admit, the fallback in this case is
rather unexpected.


Regards

Thomas

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