I am unable to send email, but I can receive.
Some Internet Service Providers will not allow you to send email using an external SMTP server therefore your email will not be able to be delivered. We have seen problems with MindSpring, Earthlink and AOL.
Try replacing your SMTP (outgoing) mail server settings with your ISP ( MindSpring, Earthlink, AOL, etc...). Leave the POP3 settings to point to your domain name so you can receive email from the server.
If you still require assistance, please open a new support ticket and we will be glad to help.