Check you are using correct Settings: https://help.astound.com/portal/articles/8523

POP:

• server name: mail.wavecable.com
• port: 995
• Connection Security: SSL/TLS
• Authentication Method: Normal Password
• User Name : full email address

IMAP:

• server name: mail.wavecable.com
• port: 993
• Connection Security: SSL/TLS
• Authentication Method: Normal Password
• User Name : full email address

SMTP:

• server name: mail.wavecable.com
• port: 587
• Connection Security: STARTTLS
• Authentication Method: Normal Password
• User Name : full email address

If Thunderbird updated then it is possible the Firewall thinks it' s a different program.

• Exit Thunderbird.
• Access Firewall
• check - Thunderbird must be set up as an allowed program otherwise the Firewal mya be blocking access to ports.
• If already set up - then block/remove it, ok it, then access Firewall again and set up Thunderbird as an allowed program.

Check via webmail for a corrupted message:

https://support.mozilla.org/en-US/questions/1158670

After many trials and tribulations......nothing helped.

Dang it.

Thanks for trying to help. Got anything else?

I'm mentioning the link below because both you and the reported at the link are experiencing issues with the same server. https://support.mozilla.org/en-US/questions/1400373

What Anti-Virus product are you using ?

Are you using AVG or AVAST ?

You could disable the Mail Shield to test if everything works when it's switched Off.

Maybe you need to sort out the Certificate - see some info: Lots of good info.

• https://support.avg.com/supportarticleview?l=en&supporttype=home&urlname=troubleshoot-invalid-avg-antivirus-email-certificate

The link above also shows where it is in Thunderbird, but it's not been updated for version 102*, so where you see it mention 'Options' assume the word 'Settings' is now used.

Thunderbird certificate area:

• Menu icon > Settings > Privacy & Security
• scroll down to 'Security'
• There is a 'Certificates' section and a 'Manage Certificates' button