1. Check if login procedure is working correctly. Also 
check if you can retrieve/reset your password using forgot 
password link (the whole procedure)
2. Check if there is a proble in the procedure that takes 
the user to inbox (after login).
3. Check whether you can delete/flag particular messages.
4. Check if message search is working.
5. check if a message (source)can be added the spam list 
and then try to send a mail from the same ID.
6. Test the usability options like font / background / 
bold/italics/alignment
7. Reply/reply all to a particular message and check if the 
reply includes the original mail or not

8. Add an attachment higher/lower than the allowed capacity
9. Forward a message with attachment to ensure that whether 
or not the attachment is included with the message
10. Access other msn network links and then try to come 
back to your inbox
11. Select particular messages and press delete
12. Select save a copy in sent folder and see if the sent 
messages are being saved there
13. Check the appearence on different browsers
14. specify wrong password three times and the account 
shall be locked out/word verification screen shall appear