I think it's more likely that church practice doesn't meet internet expectorations (lack of opt out and bad emails not being removed from the list). At some point, the email providers stop working with the sender and just black list them.
I remember when Send a Message started, the church tried to spoof the sender's email rather than using "Reply to".
It's also quite possible that the first tier support at zoho doesn't know what filtering might be taking place. If there was none at all you'd probably have more "Nigerian prince" emails than valid ones.