There are many reasons why you may not be able to send email, but the three most common reasons are:
1.) You are not using the correct SMTP server. Your SMTP server should be set to smtp.domain.com (where domain.com is the name of your domain). If you’ve recently registered your domain and want to begin using our SMTP server immediately, please use smtp.superb.net as your outgoing (SMTP) server.
2.) Your username and/or password are incorrect. If you are repeatedly prompted to enter your username and password, please ensure that you are using the correct information. Your username is your entire email address (e.g., “firstname.lastname@example.org“, not just “user” – this is a very common mistake), and your password is the same as your incoming mail password. If you forgot your password, you can reset it using the myCP -> Email Admin -> Users -> [user] page.
3.) Your ISP is blocking port 25. To prevent spamming, many ISPs are now blocking connections to port 25. Please try changing your outgoing (SMTP) server port to 587.
If none of the above works for you, please submit a Support Ticket providing the exact error message you encounter and we will be happy to assist you.