change email from pop3 to imap

I currently have pop3 as the email interface using outlook 2021.  Downloads work fine,  Up loads do not work 90% of the time = about 1 in 10 get through. The error code is 0x800CCC0F.     I thought if I changed to IMAP it may work better  but no matter what I try it never changes the result.  No IMAP email ever gets created.  What to do.  Email is [Edited: "Personal Information"]   any help is appreciated.  Thanks - Dave