
Tracking Down a Fifteen-Hour Email Delay from Outlook and Office 365 - Pneumaticat
https://potatofrom.space/post/outlook-email-debugging/
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pwg
RFC2181:
[https://tools.ietf.org/html/rfc2181](https://tools.ietf.org/html/rfc2181)

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.

