Why cant i change my incoming mail server to pop instead of imap

Im trying to chaneg my incoming mail to pop instead of imap but it says "the imap server pop.(myemail) is not responding. Check your network connection and that you entered the correct nformation in the Incoming mail server field." My iphone is on pop so im not sure why the ipad isnt working. I just need to be able to get and keep incomin emails on my ipad, as it does on my phone.

Thanks

Ariana