[Dovecot] lmtp: help needed

[Jason Fesler]

> migration), that can be converted to lmtp protocol, but we lack of
> information on the dovecot API for delivering in a "dovecot-way".

IMO..  use the dovecot lda.  Eat the performance hit of calling it.  Let 
dovecot-lda track all the API changes to indexes and such.  Throwing an 
extra machine at the problem won't cost much compared to the headache of 
tracking long-term changes from dovecot.