quick & dirty alternate addresses

While we're considering new header fields and new address-mapping
servers to deal with the problem of having alternate addresses, we ought
to consider how far we could get with what we already have.

Consider this:

From: "name1a <local1a@domain1a> / name1b <local1b@domain1b> /
  name1c <local1c@domain1c>" <local1a_ACE@domain1a_ACE>
To: "name2a <local2a@domain2a> / name2b <local2b@domain2b>"
  <local2a_ACE@domain2a_ACE>,
  "name3a <local3a@domain3a> / name3b <local3b@domain3b>"
  <local3a_ACE@domain3a_ACE>

This is perfectly valid syntax today.  Non-ASCII names and addresses
inside the display-name can be represented as encoded-words, and will
display legibly in MIME-enabled MUAs (even if they are IMA-unaware).
The actual angle-addr is encoded using ACE (if necessary), not
encoded-words, and will display correctly only in an IMAA-enabled
MUA, but even if it's not displayed correctly, the user can still see
the redundant copy inside the display-name.  If one of the alternate
addresses is pure ASCII, that one could be used for the angle-addr in
order to avoid the use of ACE.  (But we still need ACE so that someone
who remembers one of the non-ASCII addresses can later type it in and
have it traverse the SMTP infrastructure.)

In today's MUAs, the user will see all the alternate addresses and can
recognize/remember the one that's easiest and ignore the rest.  When
someone replies to all, or saves an address in an address book, all the
alternates automatically go along for the ride, even if the MUA has no
awareness that the display-name contains alternate addresses.

Newer MUAs could look for display-names that obey the pattern, and
perhaps do something more intelligent, like favor the part of the
display-name whose characters are best correlated with the user's
primary script.  (But you should always have the option of being shown
the entire display-name and angle-addr, and you should be shown all of
that whenever you compose a reply.)

Of course, when the first message in a thread is composed, unless there
is an address-mapping server, the alternates won't get put in the To:
field unless they were already in the sender's address book.

AMC