I didn't [intend to] suggest getting rid of the envelope-to field from
the list of choices, but only to add an address associated with the
Sieve script to that list. I think the owner's address is at least as
good a choice for a fixed address as a system-wide one. It may be
more readable to express it as a list, e.g.:
If ":from" is not specified or is not valid, the envelope
sender of the notification message SHOULD be selected from
one of the following, at the discretion of the implementation:
- the envelope "to" field from the triggering message, as used
by Sieve;
- the address of the owner of the Sieve script;