Kinda like MS making you login to 8.1 with a MS acct (instead of local acct) to be able to use the modern SkyDrive app, and not get pestered with stupid prompts to switch a local acct to a MS acct when opening several other apps. Lame.
Thanks for the replies. I like the modern app, but unlike Outlook, there's no way to disable saving a copy of sent messages. My provider's SMTP server already saves sent messages, resulting in duplicates in the Sent folder.