IMAP not accessible through cox wifi but is through all other routes

For the past week (January 2023) my iPhone will not connect to Cox email when on Cox wifi. If I turn wifi off, the phone connects. I can also connect through webmail, on any device and on the phone through wifi connects to browser. The problem is exclusively when iPhone is using wifi. The error is "The mail server imap.cox.net is not reponding." It goes on to suggest verifying correct account info, but that is clear since it works in all other configurations.

The always helpful "support," with whom I spent three hours on the phone, in between their hanging up on me, provided the expected suggestions. In order: It's an apple problem; delete and reenter the email account; change the password. None of those work and again, that email is accessible in all other ways suggested none of those were the problem. Their final suggestion was that I use another internet provider, which was quite a suggestion from their own "customer service." 

Any (effective) suggestions of how to restore wifi access to imap accounts will be appreciated.