Posting your account password to a public forum is a really bad idea. So you'd better change your account password ASAP, otherwise the certificate issue may be the least of your problems.

Yes that was a dunmb thing to do. Thanks for the heads up. I deleted the image

All I am trying to do is get back Thunderbird email that I have used for several years on the Mediacom server that I have used for decades. But I get the attached error message although I am using the same username and password that allowed me to lock on to my Thunderbird account and download and install the Thunderbird email program. I really liked Thunderbird over the Windows Outlook and Mail email programs.

You will need to manually configure your account if Thunderbird fails to detect the correct server settings. https://support.mozilla.org/en-US/kb/manual-account-configuration

Note, you'll have to obtain the correct server settings for your email provider prior to setting up the account. So either talk to your email provider or check their support site for the required settings.

You may also post them here (or a link to the support site) if you're still running into problems.