This has been known for a while about Yahoo account's downloading everything. Me I just can't understand why people leave everything in there inbox's. all I can say about that is learn to use FOLDERS, clean out your e-mail and keep your Inbox lean. and there are lots of ways to archive Text messages, do people really need 2000 texts stored on there phone?
Myphone works great for archiving text's.
There is also a program over at XDA to archive your text's to your e-mail.
http://forum.xda-developers.com/showthread.php?t=702390