Let's throw some acronyms around, just for fun. Some ISPs (Internet Service Providers) recommend that their clients use the Outgoing SMTP (Simple Mail Transfer Protocol) server of the ISP. This is SOP (Standard Operating Procedure), and you need to contact your ISP to determine what is the proper SMTP configuration. This would normally include the SMTP address, as well as a username and password. But in reality most people use our SMTP server, which is just simpler. You can do that if you want. Our Outgoing SMTP server is the same as the incoming mail server, e.g. mail.yourdomain.com (replace yourdomain.com with your actual domain).
If you use our SMTP server for your outgoing mail, you need to make sure that you "authenticate" to the server, just like you do when you receive the mail. This is how we make sure no one else uses the server to send out SPAM. So usually there is an option in the account setup, where you enter the outgoing SMTP server address, and you have to check a box that says something about the server requiring "Authentication". You then enter the same username and password that you use to receive incoming mail.
If you can receive email, but you can't send, the problem is with your SMTP configuration. It's probably a simple typo or missing authentication. We can't see your configuration so we can't really help. It's really beyond the scope of what we can support, so you should try to find a local tech person, or technical friend to help you look at the settings. It's quite simple really if you just read the options.
If you think there is something wrong on our end, we will be glad to help you. But please follow some basic support guidelines and try to provide us with all the information you can: