Whether I use outlook.com OR a client (e.g., Thunderbird or OS X Mail), there are two copies of every e-mail I send out that get stored in the Sent folder.

It gets better: I don't notice this when using OS X Mail, so I'm fat, dumb, happy. However, in T'bird, when I look in the Sent folder, there are two copies of every message.

"More" better: in outlook.com, the two copies have different names attached. One copy always has the intended recipient, as indeed it should. But the duplicate shows it as Sent TO ME! Of course, it's NOT being sent to me, but one could be lead to believe that.

Any ideas, good and gentle people?