Add a better error message when trying to update an IMAP/SMTP endpoint.
Add a better error message when trying to update an IMAP/SMTP endpoint.

jobscore/sync-engine,jobscore/sync-engine,jobscore/sync-engine,nylas/sync-engine,closeio/nylas,closeio/nylas,closeio/nylas,jobscore/sync-engine,closeio/nylas,nylas/sync-engine,nylas/sync-engine,nylas/sync-engine