If you internet connection is up then you are experiencing with cache problems or over limit size (outlook)
for out look:
if you can not send email and server is up means you are out of limited size so you need to create new pst file.
how to create new pst file?
a. Click on tool menu
b. select email accounts...
c. check mark on view or change existing e-mail account then click on Next
d. Click on New outlook Data file..
e. select Office outlook personal folders file (.pst) and click on ok
f. locate your pst file (by default it goes on outlook folder or exchange
g. click on ok
h. Give your personal folder name then click on ok.
i. now selet your new personal folder from "Deliver new email to the following location" just click on drop down button and select your new created folder one.
j. click on finish and close your outlook and restart it.
if you have problem sending email on hotmail, yahoo or google then you need to clean just cache
how to clean caches ?
Right click on your internet explorer icon>Properties
Delete cookies, delete Files and clik on ok.
one more thing
Click on start>run and type in "prefetch" without qouets.
and press CRTL+A and delete all availabe files (junk caches for windows).
now reboot your pc and that's it.
Good luck and rate all answers.