have you tried disabling your antivirus product. Most interfere with internet connections and truly mess up email by using their own self signed SSL/TLS certificates

This is the only relevant image here, it has a view button and what that reveals with show what source the dodgy TLS certificate has. My guess is it will say something about Norton or McAfee or some other antivirus product that has not bothered to have their business audited as required to be automatically included in the chain or trust and a certificate issuing authority. Next is your choice of deciding if you trust them to certify your connection encryption. Personally I use Microsoft Defender. No dodgy self signed certificates there and it costs me nothing.

Thanks Matt for the prompt response,

   Image #1 was from Wife's account that is working. My account didn't post this "Add Security Exception"

screen. Only thing to my account is Image #3 above. No "View" button and no Error Exceptions either. No Norton or McAfee or some other antivirus product on either box, only Microsoft Defender.

 Image #2 above is from wife's account and when press "view" get the below image #1. It has several sections

of "Stuff" and 3 tabs that I don't really understand. But here one can see the date of the issue starting, Fri May-30.

 This exception worked on Wife's PC but not mine. Any way to reload, bypass, reengage or reissue with 

cert, etc.? Any other thoughts on what I could try?

thanks in advance,

Gene

Matt,

  Attempting to "Add Exception" to my config Under [Settings/ Privacy & security / Manage Certificates]

Fig 1 below. I try the following URL's and note the responses to each https://mail.charter.net URL From the wife's working Security Exception (fig 1 right above)

    Results in Fig 2 below - unable to obtain.....

https://pop.charter.net URL From viewing exceptions in wife's PC

   Results in Fig 2 below - unable to obtain.....

https://mail3.charter.net URL from Web Browser to e-mail (this currently works in browser)

   Results in Fig 3 below  - see it but, unable to obtain.....

https://secure.globalsign.com/cacert/gsrsaovssl2018.crt (from wife's certification)

  Results in Fig 4 below  - No need and can't "Confirm Exception"

https://secure.globalsign.com/gsrsaovssl2018 (from wife's certification)

  Results in Fig 4 below  - No need and can't "Confirm Exception"

Again, any way to work around this other than uninstalling TB and reinstalling it? (several hours I'm sure)

thanks Gene

I think you have to use the recommended settings:

incoming IMAP server: mobile.charter.net, 993, SSL/TLS, normal password, email address

outgoing SMTP server: mobile.charter.net, 587, STARTTLS, normal password, email address

https://www.spectrum.net/support/internet/email-settings/

I've seen references to these POP settings: pop.charter.net, 110, SSL/TLS, normal password, email address, but the standard SSL POP port is 995. I don't know if Spectrum/Charter still supports POP.

Thanks sfhowes & Matt,

 After reviewing the link you provided and other links to Spectrum/Charter server configuration, I did:

1) Screen copied everything from Account Settings - a "backup" button to do this would be very nice or

   a file that contains the Account Settings specifics vs. tedious snipits of each section of each screen.

2) Screen copied everything from Settings - ditto on a "backup" button 3) Backed up Addresses, filters and calendar 4) Went into Account Settings / Highlighted the problem account

   Then Account Actions / Remove account
   Followed carefully the delete screens and made sure to not disrupt my TB file stuff
   If removed the account, I wanted to retain the Original Dir's for Server file tree and Local file tree & msgs

5) Then Account Actions / Add Mail Account

  I used the new Spectrum server settings IMAP, mobile.charter.net, port #s, etc.

Working now

  I have some clean up, like mapping Local Dir, New Account Dir to point to prior install dir's
 Check out things like message filters, etc.

But, I can send and receive mails using SSL/TLS w/Password!

thanks again guys, Gene

Mail & News Accounts in Help/Troubleshooting Info has account settings.

Local mail in mbox files (no extension, named after folders) in Mail/<popservername> can be copied to Mail/Local Folders, with TB closed. Also, filters stored in msgFilterRules.dat in Mail/<popservername> can be copied into ImapMail/<imapservername>.

Thanks sfhowes,

  All good to know for next time.....

I did lose the "Drafts" and "Template" Dirs. I viewed My Dir tree looking for them, found them, but zero size So it is..

 Other than than that, back online with SSL/TSL and a password!

thanks again,

A residual from ALL of the above When making a calendar event, the "Notify Attendees" is grayed out (image 1 below) and can't check it found this https://support.mozilla.org/en-US/kb/inviting-other-people-events and this https://support.mozilla.org/en-US/questions/1493320 Close, but not closing out the issue. Anybody have any ideas? TB rev 128.11.0esr (64-bit)

Goto Calendars

  Select and Right click on the target calendar

Add e-mail as requested Image 1 below