Multiple IMAP accounts cannot be set up using same server name

New iPadAir4, 256Gb, 10.9 inch screen. I own a business and use mutiplle IMAP emails associated with my server, such as info@----, contact@----, sales@----. Once I set the first email address up and it is verified, the iPad will not allow a 2nd or subsequent email address using the same host server name to be set up. It states "This IMAP account has already been added by your iPad." Meanwhile, a separate non-associated IMAP email address and a POP3 address can be set up which come from internet providers. I have been on the phone 3 times for 4+ hours yesterday with Apple Support. I have reset the iPad, gone through a million steps of setting, re-setting, erasing, re-setting..and finally trashed my entire iTunes back-up restore files of 18k photos, etc; to get back to a bare-bones iPad, attempting to set up the email accounts first of all. No dice. The IMAP problem persists. Apple Support is now suggesting re-installing the iO/S14.4 software but I am not confident that this will do anything. I do have all these mutiple IMAP accounts operating fully properly on 2 Apple Mac Minis, and a MacBookPro, and had them running on my 7 year old iPad2 (which was also using the same iO/S14.4) until 24 hours ago, when I changed to the new iPad Air4. This indicates that I know what I am doing and that there is nothing wrong with my host server, those IMAP email addresses or set-ups. Thanks for any suggestion!