Can receive emails, but not send.
Typically that may be caused by something interfering with the connection. As a test, can you completely disable any anti-virus, firewall, proxy or VPN, then try send again. Sometimes even restarting your router may resolve this.
But it can be because of incorrect settings, or some server issue.
If you send a message, and it fails, go to Menu > Operations > Log tab and look for the SMTP error. It will give more information.