If you can receive emails on your account but cannot send emails it may be for one of two reasons:
1. That the email routing for your domain is not set correctly.
Check to see that the Email Routing is set to Local Mail Exchanger.
More details are contained in the following Knowledgebase article: What is the difference between Local, Backup, and Remote Mail Exchanger for Email Routing?
2. That your ISP is blocking you from sending emails using anyone's outgoing mail servers but their own.
Many major ISPs block outgoing emails on Port 25 to prevent their internet connection from being used for spam.
To overcome this common issue and allow you to send emails we also use Port 26.
So if Port 25 does not work please try changing the outgoing mail (SMTP) to Port 26.
1. If you use Outlook, please ensure that you select the option for "Outgoing SMTP Server Requires Authentication" as this is required by our servers for security reasons.
2. If you are trying to use Windows 8 please read the following Knowledgebase article, Problems setting up email on Windows 8.