My first thought would be to run the Mail Protection Wizard again. Since you uninstalled Avast and reinstalled, the Avast .ini file needs to be configured.
What email client are you using?
If you use the Help file from the main Avast interface, look up Manually configuring email protection. It will explain how to check the settings of the email client.
If you can receive and not send, then it might be the SMTP server address, or an authentication error.
techie