Maybe the standards documents you are used to differ from RFCs, but here is the official language:

   3. SHOULD   This word, or the adjective "RECOMMENDED", mean that there
      may exist valid reasons in particular circumstances to ignore a
      particular item, but the full implications must be understood and
      carefully weighed before choosing a different course.

SHOULD is effectively REQUIRED unless it conflicts with another standards requirement or you have a very specific edge case.

▲ jcelerier 3 hours ago | parent | next [-]

I just don't understand how you get from the text you pasted to "required". Nowhere does it say that anything is effectively required. Words have meaning.

▲

nerdsniper an hour ago | parent | next [-]

> the full implications must be understood and carefully weighed before choosing a different course.

In this case, the full implication is that your email might be undeliverable. "Should" indicates that the consequences for this fall on the entity that is deviating from the thing they "should" be doing.

▲

zdragnar 2 hours ago | parent | prev [-]

> the full implications must be understood and carefully weighed before choosing a different course.

Note the use of the word "must" used twice there. Barring a sufficiently good reason and accepting the consequences, this becomes a very poorly worded "required".

The spec would have been far better starting with SHALL and then carving out the allowance for exceptions.

▲

shakna 2 hours ago | parent | next [-]

No, its not a "required"... It means someone may have reasons not to use something, and so spec implementors need to allow for circumstances where it is not present.

Those reasons can be anything. Legal, practical, technological, ideaological. You don't know. All you know is not using it is explicitly permitted.

	▲	zephen an hour ago \| parent [-]
		> You don't know. All you know is not using it is explicitly permitted. In theory, if they are truly following the specification, you know they thought hard about all the consequences. I think the pushback in the comments comes from the commonsense feeling that this... didn't happen here.

▲

WJW 2 hours ago | parent | prev [-]

I don't even know how you got to "used twice" tbh. Both your own comment AND the post you quoted from only have a single "must".

The only thing that text demands is understanding and carefully weighing the implications. If, having done that, you conclude that you don't want to then there is absolutely nothing in the spec stopping you. Maybe the spec would have been better off putting more stuff in SHALL and less in SHOULD, but as written that is definitely not the case.

▲ BeetleB 2 hours ago | parent | prev | next [-]

Nope, it's exactly what it says: RECOMMENDED.

Any time any document (standards or otherwise) says something is recommended, then of course you should think it through before going against the recommendation. Going from their verbiage to:

> SHOULD is effectively REQUIRED unless it conflicts with another standards requirement or you have a very specific edge case.

is a fairly big leap.

▲ andoando an hour ago | parent | prev [-]

required means it must exist, not that it may or may not exist depending on the reason