Can't send e-mail using my @me.com account but I can receive them

I share your concern and problem...it has happened to me multiple times in 10.8. Possible fixes: go to Library and find the com.apple mail
and trash it and restart. Enter Acccount information again.Make sure your outgoing is: icloud selected and select use only this. AppleMail is a flawed program and needs to be updated Among its problems are:
unable to delete some emails (am experiencing that today) unable to control a, select all junk and delete anymore.
Make sure your email to address is accurate. If this does not work, call AppleCare if U have that service. Apple is more interested in us posting more pics to Facebook, share stuff with your Apple phone (you do have one don't U?) and iPad...I am sure we all have one!!Basic applications are of not much concern.

 

Do you have the smtp server configured? If not, that would explain why you can receive but not send. Do you have any other accounts set up on the Mac?

 

With applications quit..not running. Find "go" pull down menu
on upper left. pull down menu and hold down option key..Library
will pop up in that menu, then select and go to preferences.
Find com.apple.mail...drag it and put into trash, restart

 

It sounds like it is configured. Try unchecking the "use only this server" box. This should allow you to select a different smtp server when composing and sending a new email via a drop down box in the compose window. Try sending an email with your hotmail smtp server and see if that works. If it does, then it means that something is configured incorrectly with your iCloud server.

 

help

If U still have apple care call them
If U do not have it see if U can buy the extension of time of apple care