depending on who your email provider is, they may have changed something on their end.

for instance I have att.net email address, but it turns out it is actually yahoo mail.
They added a layer for security and I can no longer use my att.net log in to get mail from my outlook program. I have to go in and generate a new password just for my email program to log into the smtp server to get my mail.
took me forever to figure it out.

you will have to verify at your providers home page and see what they say about email setup and make sure your program does what they need. see if you can see it via a browser instead of a mail program.
they could have also changed ports or it could just be down today.
lots of possiblities.