On 2020-03-31 10:13, Andreas Fink wrote:
> your reverse DNS is not matching for 157.161.57.26 as it returns 
> aleka.scout.ch.
> 
> list.scout.ch. is not the same as aleka.scout.ch
> You could do instead
> 
> 
> list.scout.ch  MX 50 aleka.scout.ch
> 
> or 
> 
> list.scout.ch  CNAME aleka.scout.ch.

Please, please, please, for your own sanity: NEVER EVER point an MX to a CNAME.


Sendmail, which some people still use (oh heck my inbound MX's are sendmail), 
will mess up the domain that way and nicely replace it.

Thus a mail to: someth...@lists.scout.ch would be replaced by sendmail with 
someth...@aleka.scout.ch, which likely will not end up in the same place, and 
will cause other expected.



Also RFC refs why not to do it:

https://tools.ietf.org/html/rfc1912#section-2.4
8<----
Don't use CNAMEs in combination with RRs which point to other names like MX, 
CNAME, PTR and NS.
...
----->8


http://tools.ietf.org/html/rfc2181#section-10.3

8<----
10.3. MX and NS records

The domain name used as the value of a NS resource record, or part of the value 
of a MX resource record must not be an alias. Not only is the specification 
clear on this point, but using an alias in either of these positions neither 
works as well as might be hoped, nor well fulfills the ambition that may have 
led to this approach. This domain name must have as its value one or more 
address records. Currently those will be A records, however in the future other 
record types giving addressing information may be acceptable. It can also have 
other RRs, but never a CNAME RR.
----->8

and there are others that detail this problematic setup.



In general actually: avoid CNAMEs where possible; just pre-process your records.

Greets,
 Jeroen



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