[Dovecot] best choice of user database file to work with postfix

[Ed W]

P.S.  The "idiot" who kept breaking the plain text format file in my 
original setup was .... da da ... me ... So given I think of myself as 
reasonably technical, I would claim that text format "databases" are way 
more fragile than you might expect.... (good luck getting a non 
technical user not to break the text format file from time to time...)