LOL. Yeah that’s the issue. 
Pushing this back to the top again.
The scanning of inbound emails is the specific option that blocks Thunderbirds IMAP connection.
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maybe your computer broke? [quote=“sssleepingvr4, post:1, topic:773578, full:true”]
Avast’s mail shield is blocking IMAP on Thunderbird. As soon as I disable the mail shield Thunderbird works normally.
Is there a resolution to this? SIM
[/quote]
I got the same problem upon installing Avast Premium. I discovered the same solution after many trials in Avast settings (before searching this forum).
This problem occurs with Avast, not several other AVs.
FWIW I do not have this issue. Win10 Pro 22H2, Avast Free 24.6.6121, Thunderbird 128.7 ESR channel. No problems with IMAP access to Hotmail/Outlook, Gmail, Yahoo Mail, and Mail.com accounts. Settings as shown. I routinely disable SSL scanning, though I can’t say that is the cause of these problems.
Have been using Avast and Thunderbird for many years. This problem is now occurring for us. Temporarily disabling Avast shields allows mail to come through, and oddly now continues coming through after the shields are re-enabled. However, Thunderbird still fails on attempting to copy sent messages to the server Sent folder. We’re on a hosted email account for our domain. Thunderbird throws errors about the certificate being invalid and asks to add it as a permanent exception but this does not solve the error. I spoke with our hosting rep (the actual owner of the company as it’s a small local operation) and there have been no email server changes. Confounding.
@Avast_Admin