I have just purchased a Windows 8.1 desktop computer and set it up using my personal Xtra (pop3 server in New Zealand) email address as my Microsoft account.
I then upgraded to Windows 10. I've been able to set up my Gmail, my work email on an Exchange server and another Xtra account I have and they all work fine in Mail. The email address I used to set it up is the only one not working. It automatically loaded into Mail and all of the emails loaded but I can't view them - I get the message "Download message and pictures (45.2KB) or similar KB depending on the size of the email. I'm also not always able to look at any of the settings for this email account - they are sometimes greyed out, but not always.
I have since uninstalled Windows 10, changed my login to an outlook.com email address and reinstalled Windows 10. The outlook.com email set itself up in Mail and shows all emails fine. I then added all of my email accounts again. They all added fine to Mail and the 2 Xtra accounts added also. However my personal Xtra account still loads all emails but I can't view them and I still get the message "Download messages and pictures"(....KB). I've gone online and was able to look at the emails through Yahoo and know I have the password correct. I also know the pop server works with Mail and Windows 10 as the other Xtra email address works fine. Can you please help?