[adekok]

Having written multiple RFCs, violating the RFC is not always a bad thing. Some of the MUSTs are a result of the committee process, and follow the lowest common denominator.

If the recommendations don't make sense, don't follow them.

[jlgaddis]

> If the recommendations don't make sense, don't follow them.

In general, I would tend to agree -- so long as you aren't "hurting" (affecting) anyone else.

OTOH:

  $ tail -n 4 ~/.signature

  "The total budget at all receivers for solving senders' problems is
  $0. If you want them to accept your mail and manage it the way you
  want, send it the way the spec says to."  --John Levine

I'm responsible for a bunch of mail servers and occasionally get reports that messages from some random sender to a mailbox on one of these servers is not being accepted. More often than not, it's because RFCs aren't being followed (WRT SMTP, I'm not very liberal in what I accept). Of course, they will demand that I "fix" my "broken" servers that are refusing to accept their messages. Sometimes the non-compliance is intentional but usually it is simply out of ignorance (especially true when the remote host runs Microsoft Exchange); I try to point them at the RFCs, explain why their mail is being refused, and what they can change so that the mail will be accepted.