Please send a screenshot of any error messages that are popping up.

Thanks for your feedback. There is no error message popping up. I can send emails, but I can't receive. The problem is with incoming mails. Thank you.

What text are you getting at the bottom left of the program when you try to download manually. Does it connect to the server? Does it say there are no messages to download? What is it reporting?

Thanks again. When I tried to download manually, here is the error message The certificate for pop.domainname is not valid for that server. Someone could be trying to impersonate the server and you should not continue.

I take it that you have obscured the name of the server - so I can't check the name of the provider. Please access your Email Provider's web pages to check the correct connection settings. They may have altered the servers or ports.

However, as it talks about a 'certificate', it is probably informing you that the security certificate for the server has now expired and lapsed so that Thunderbird cannot be sure that it is secure to make the connection to.

Usually, a message like this asks whether you wish to override the warning and, personally, I wouldn't. I would be contacting the Email Provider to find out what's going on.

Thanks again. I obscured the name. Let me give it to you again. The certificate for pop.msnucleus.org is not valid for that server. Someone could be trying to impersonate the server and you should not continue.

Yes, exactly. TB is issuing you with a warning that the certificate being offered as authenticity, safety and security for that server is *not valid*. It's warning you not to continue. All the error messages I've seen like this normally give an override button but, honestly, I wouldn't click on it. I'd be contacting my Email Provider.

Thank you!!! It is resolved now!