There is most likely a problem with your settings.
Here are some places to troubleshoot:
Using the correct outgoing port?
Make sure your outgoing email (SMTP) connection uses port 587. By default, the port is set to 25. However, email sent through this port will be arbitrarily blocked due to all the spam that also gets sent using port 25. Your email will sit in your outbox, sometimes for hours, and then suddenly send. As an alternative to 25 we have port 26 for non SSL connections.
Need different outgoing servers?
Some high-speed internet service providers require you to use their servers when sending email. If you have such a setup, when you send email it is not going out via your HostPapa account (even though it looks like it does to anyone who receives the email).
If you do have different outgoing servers, check the rest of your email program settings. Your outgoing settings are correct, but there may be something wrong with your incoming settings.
Connecting to the default email account?
The default email account is not a fully functional email account, and cannot send email. It is possible to accidentally connect to it. Your email username is the full email address including the @your_domain.com. Please do not use your cPanel username, as this will connect you to the default email account.