[Dovecot] Configuration of LMTP Reject Code

[Petter Urkedal]

Is it possible to change the reject codes from the Dovecot LMTP agent?
In particular I would like to change the "550 5.1.1 <...> User doesn't
exist." to a temporary failure, since we already validate email
addresses on the mail front-end, and such errors are most likely due to
a temporary glitch in the user database lookup.

We use Postfix on the front-end, which is very configurable in this
respect.  I don't see a way to override the error code from LMTP,
though, but suggestions are welcome.