RFC Errata
RFC 1123, "Requirements for Internet Hosts - Application and Support", October 1989
Note: This RFC has been updated by RFC 1349, RFC 2181, RFC 5321, RFC 5966, RFC 7766, RFC 9210
Source of RFC: Legacy
Errata ID: 6134
Status: Rejected
Type: Technical
Publication Format(s) : TEXT
Reported By: Abel
Date Reported: 2020-04-28
Rejected by: Barry Leiba
Date Rejected: 2020-04-28
Section 5.2.2 says:
5.2.2 Canonicalization: RFC-821 Section 3.1 The domain names that a Sender-SMTP sends in MAIL and RCPT commands MUST have been "canonicalized," i.e., they must be fully-qualified principal names or domain literals, not nicknames or domain abbreviations. A canonicalized name either identifies a host directly or is an MX name; it cannot be a CNAME.
It should say:
RFC5321 Section 2.3.5. Domain Names Only resolvable, fully-qualified domain names (FQDNs) are permitted when domain names are used in SMTP. In other words, names that can be resolved to MX RRs or address (i.e., A or AAAA) RRs (as discussed in Section 5) are permitted, as are CNAME RRs whose targets can be resolved, in turn, to MX or address RRs.
Notes:
Section 2.3.5 from RFC 5321 seems to contradict the section 5.2.2 from 1123.
In RFC5321 it is implied that you can have a domain CNAME pointing to another that has an MX record that is not a CNAME and it should work. However 1123 states that it's not possible.
--VERIFIER NOTES--
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