If ":from" is not specified or is not valid, the envelope
sender of the notification message SHOULD be set either to the
envelope "to" field from the triggering message, as used by
Sieve, or to a fixed email address (so it "comes from the
notification system"), at the discretion of the implementation.
already list all possible alternatives, so I don't think it is a
SHOULD either.
Those aren't all possible alternatives, so although I don't mind MUST
I rather like keeping SHOULD. (One other alternative is a system
address with a single-use subaddress.)
Ok, you and Barry have convinced me that this SHOULD is fine.
Also, how about deleting the word "fixed" above?
"Fixed" does indeed not hit the point, but do you have a better
suggestion?
The idea was to allow the system to used a fixed address, or a fixed
addressing scheme, no matter if the variable part is a RFC subadressing
detail or some other kind of subadressing, that can be recognised as such,
telling the mail "comes from the notification system". The quoted part
tells exactly what was tried to express. I would appreciate a better
wording, but can't think of any.
It is definitively a SHOULD, if we can't even specify it sharply.
Michael