Diagnostic Code: 550 Mail rejected by <Zoho Mail>

We have no control on why different mail services block us, and unless the messages from their mail servers are explicit there is not much we can do.

What we are finding is that many club are not removing people from the mailings after they left and then the people mark the FTH emails as spam. Also we are finding that members rather than deleting emails from FTH they don't want mark them as spam. All members have control over what emails they receive from FTH in their profiles but the site admins don't seem to do much training.