> On Nov 17, 2019, at 8:35 PM, Mark Andrews <ma...@isc.org> wrote:
>
> Just because broken configuration don’t always cause problems doesn’t mean
> that they don’t sometimes. MTA’s need to know what names they are known
> by to properly remove MX records from consideration when performing store and
> forward. Email forwarding loops still occur.
Postfix ignores the names, and does loop elimination by IP
address. It also detects loops when it sees its own name in
the 220 banner or EHLO reply. Relying on just canonical names
for loop elimination is not enough. The same IP address can
can have multiple names even without CNAMEs.
Other MTAs may look at the names and not the addresses, but
I would hope that they also employ additional loop detection
mechanisms, and there's ultimately the hop (Received header)
count.
--
Viktor.
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