Currently if saving to mailbox fails for any reason, the mail is saved to INBOX
instead. Same if a Sieve redirect fails, the mail is saved to INBOX. I'm
wondering if anyone actually prefers this behavior when the error is temporary?
For example if some index file corruption was detected, the save will most
likely succeed the next time it's attempted. Or if the redirect fails because
the SMTP server can't be connected to at the moment. So I was thinking about
changing v2.2 LDA/LMTP to simply return temporary failure instead of saving the
mail to INBOX.
