[vox-tech] some people can't send to list

[Rick Moen]

Quoting Brian E. Lavender (brian at brie.com):

> Hey, so word is that some can't send email to the lugod lists because the
> mailserver the MX record is a CNAME rather than an A record?

That is known to be a common problem.  I hear there are a number of
MTAs that refuse to deliver to RFC-noncompliant sites.

People relatively new to maintaining DNS zonefiles tend to drastically
overuse CNAMEs, I notice.  My own recommendation is to _never_ use a
CNAME for any use-case in which an A record will do the job -- because an
'A' record will never get you into trouble in exactly the situations
where a CNAME can (MX and NS records), and because overuse of CNAMEs
tends over time to create a tangle of indirect reference.  That tangle
can then lead to further problems, like removing an 'A' record but
forgetting to hunt down and repoint the CNAMEs resolving to it.

There is exactly one use-case that actually requires a CNAME:  pointer
to an 'A' record in a different DNS zone.  I personally use them for
that function _only_, and nowhere else.

Some readers may be thinking 'But the advantage of my CNAMEs is that I
only need to update an IP in one place.  Using A records instead, I'll
have to update the same IP in lots of places.'  Correct -- but smart
people use sed (or equivalent).  Which means it's the same action to
update an IP in hundreds of lines as on one line.

Avoiding CNAMEs where such are not necessary also eliminates multiple
DNS lookups.  In that sense, unnecessary CNAMEs are like unnecesary
symlinks.

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