For almost two years now, every few months, a user email address gets blocked by Zoho. The painful business consequence is that the user does not receive @mention email notifications.
Sometimes several days pass before another user notices, by which time, and some negative consequence has occurred, and which must be repaired.
We aren't using CRM for mass-email marketing. Our external MX provider is Yahoo.
What are we (or Zoho) doing wrong to cause this recurring pain?