Are you able to receive emails but not send?
If you can receive mail but arent able to send this means one thing.....
Your internet provider is blocking you from using anyones outgoing mail servers but their own. Many major ISPs are blocking outgoing emails.
The reason they do this is to prevent you from using their internet connection for spamming purposes.
You will still be able to send emails, but only by using your ISPS outgoing mail server.
Every ISPs outgoing mail address is different, but for the most part they will be mail.yourispname.com
For example, if you had hosting with AOL.com, their outgoing mail server would look like this: mail.aol.com If mail.yourisp.com does not work and you are still unable to send emails, you will need to call your internet service provider to find out what their outgoing mail server is.
*** The above information is for reference only, Please seek independent technical advice if found necessary.