[GLLUG] ipv6, privacy addressing, and mail servers.

Tim Woodall t at woodall.me.uk
Thu Nov 22 08:42:03 UTC 2018

Hi all,

In one of my replies yesterday, the cc has been bounced - actually it's
temp-failing but I'm assuming it will bounce.

My mailserver is einstein.home.woodall.me.uk. That resolves to four
addresses, all of which resolve back to einstein as expected.

But that host is using privacy addressing. So the ip address that it
uses to connect is merely in the same /64. (Assuming ipv6)

The target mx in question is trying a reverse lookup, that is failing,
and then the mx is temp-failing my email.

What is the 'correct' behaviour?

1. I don't want to change privacy addressing - this host also runs a
squid proxy and I like that the address it uses isn't suitable for
connecting back to me.

2. I could add a wildcard PTR record to einstein - but like 1, this
makes it easier to determine what address to connect back to me on.

3. I could add a wikdcard PTR record that has no matching AAAA record -
no idea whether this would resolve this issue or not.

4. Just say that the target MX is badly configured and ignore the issue.
With a handful of exceptions, I'm of the school of thought that 'if
your mailserver doesn't want my email then I'll respect that and not
bypass your filtering'

(But I'm not sure if the IP used by a mailserver should always have a
PTR record or whether it's just the EHLO host)

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