I can receive emails but I cannot send them.

I cannot send an email. I can receive fine, but when it tries to send something, it says it there is a problem, that it can’t reach the server. I ran diagnostics on SMTP and after testing and fixing it, it said it should be alright. Still not sending though. What can I do?

I use Comcast as my email provider. Also, the Host for SMTP is already filled in correctly.

I am not sure but I think that Comcast has changed something regarding SMTP recently so I would ask their support for more information first.