Yahoo Mail Archiving. It’s about time, but Yahoo plus mail accounts lets you archive old messages. Yes, you can archive Sent messages, as well as any subfolders you have created.
First, it is un-fucking-believable that it took 4 years to come up with that feature.
Second, this is a major feature to yahoo mail. They should promote it more.
Third, this addition has now simplified the archiving problem considerably.