Email Clients Suddenly Unable to Connect to BlueHost

I am suddenly (as of a few days ago) unable to connect to the email servers at BlueHost using any of my email clients (AirMail, Apple Mail, Spark). I can log in to BlueHost and send/receive just fine directly via webmail, but much prefer to keep things integrated with my iCloud email through one Mac OS/iOS client.

I have spent many hours with BlueHost technical (ahem) "support," but they can tell me nothing other than what I already know: the network server settings. They finally asked me to call my ISP (MetroNet) to see whether there was a problem on that end.

My only clues:

I have dynamic IP address through Metronet — could the BlueHost servers suddenly have decided they don't like a shifting IP address?

When I look myself up on WhatIsMyIPAddress.com I see that Apple's Private Relay is appearing as a VPN:

Could that be causing the problem?