Email Syncing Issues

My Cox email no longer syncs (emails deleted on one device are deleted on all other devices).  I’ve deleted and re-added email accounts.  Problem remains.  Also, my iPhone’s incoming email server is pop.cox.net.  My Ipad(s) incoming email sever is imap.cox.net.  I’ve manually changed my iPhone’s incoming email server to imap to match the ipads but it reverts back to pop.  What needs to be changed.  Running the latest IOS on all devices..