I agree that the envelope-to is the best choice if the application
hasn't been configured to use a fixed address. But I also think that
having the only choice for a fixed address be a system-wide one isn't
fine-grained enough. So maybe instead of "the address of the owner
of the Sieve script", more like:
- an email address associated with notification messages sent on
behalf of the email-address receiving the message;
and it's up to the implementation how that association is made, or
whether it's made at all. One could actually interpret that to cover a
system-wide address, as well, maybe with some slight fiddling, so that
the other choice (the "email address associated with the notification
system") could be dropped.
How about that?
If ":from" is not specified or is not valid, the envelope sender of
the notification message SHOULD be set to an email address associated
with the recipient or the notification system, at the discretion of
the implementation (common choices are the final envelope recipient
or a fixed, system-wide sender).
Widen it once more and I suggest "... SHOULD be set." (no more ;)
Michael