[MlMt] don't like auto-add

[Randy Bush]

>> i have too many imap mailboxen already.  i am not happy that, if i
>> compose or reply, i get subscribed to Sent, Drafts, whatever in
>> Sources.  can i stop this from happening?
> 
> MailMate has to put emails somewhere when creating drafts or after
> sending. You can assign which mailbox MailMate uses using the “Mailbox
> ▸ Mailbox Type” menu item (for each account).
> 
> I guess the answer is no then, but I might not have understood the
> question correctly. What you would you like to happen to drafts and
> sent messages?

my issue is not that Sent/Drafts/... exist.  i just do not want to be
gratuitously subscribed to them in SOURCES.  the issue is screen real
estate.

randy