[MlMt] SpamSieve "good" mailbox not being synchronized

[Steven M. Bellovin]

Per the SpamSieve instructions, I have a "good" mailbox to which I move 
messages that have been incorrectly classified as spam.  This allows me 
to train SpamSieve remotely.  The problem is that that mailbox is not 
being synchronized by the MailMate instance on which SpamSieve is 
running.  That machine (all of my Macs, actually) are on El Capitan and 
MailMate 5187.  Is there something else I should set?  (I seem to recall 
that it originally worked correctly.)