There are no automatic updates to 78. SO I am guessing you have an anti virus that does it for you. That is also probably the issue. Standard diagnostics to determine the cause follow.

• Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender.
• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 10, Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

Had tried both of these before but have done them again with no success still no emails arriving. I am able to send messages from my w7 machine but not receive. Working perfectly before download, can I revert back?

Thunderbird displaying wrong times on these messages or is it a different time zone?

What server are you using?

What error messages are you seeing? Tools > Developer Tools > Error Console

There has been a significant change in Thunderbird 78 which is causing a load of headache for people who are downloading from the many servers that are not currently offering TLS1.2.

It turned out that Thunderbird had decided to update to using TLSv1.2, which is good, but in the same process has stopped all access on TLSv1.0 and TLSv1.1 and this means people who access servers that are not using TLSv1.2 have to chnage their server settings in order to get connection to server.

So I checked server settings eg: 'mail.livemail.co.uk:995' at this website https://www.immuniweb.com Results say: The server has TLS 1.0 enabled. It is non-compliant with NIST since SP 800-52 REV. 2 and non-compliant with PCI DSS since the 30th of June 2018. Non-compliant with PCI DSS and NIST The TLS engine does not support a TLS version newer than TLSv1.0 and is outdated. Non-compliant with HIPAA and NIST

So actually, Thunderbird is not really to blame as it is keeping up with security standards.

But it would have more beneficial to include TLSv1.2 and keep the older versions working for all those people stuck on servers have have as yet not updated.

If the server you use does not use that up to date protocol then you have to change the server settings. I ran into same issue.

TRY: If Pop Port: 110 Connection Security: STARTTLS Authentication Method : Normal Password

If Imap Port: 143 Connection Security: STARTTLS Authentication Method : Normal Password

Don't understand much of the terms used but I am receiving emails on my w10 machine(not updated) just w7 machine (updated) not receiving since update(both desktops) emails are coming through Talktalk broadband to Thunderbird. W7 is using your recommended port 110

I've just checked the pop mail.talktalk.net:995 at https://www.immuniweb.com/ssl/?id=3RvXJQvV

It seems to say that server supports TLS1.0, TLS1.1 and TLS1.2 So your issue does not sound the same as mine.

What Firewall are you using on the W7 machine ? It is possible that the Firewall may think that the new updated Thunderbird is somehow different from the old Thunderbird and is blocking Thunderbirds access to the internet. In Thunderbird. Reset the Server Settings to correct pop settings: Pop using port 995 and Connection Security : SSl/TLS

Exit Thunderbird.

Access the Firewall and remove Thunderbird as allowed. Ok it. Then access Firewall again and set Thunderbird as allowed and ok it. Then start Thunderbird.

Windows 7 does not support the now obsolete TLS V1.0 and 1.1 so the limitation is probably the windows 7 becoming end of life. See https://support.microsoft.com/en-us/help/245030/how-to-restrict-the-use-of-certain-cryptographic-algorithms-and-protoc and https://support.cybersource.com/s/article/How-do-I-enable-TLS-1-2-on-Windows-7

Perhaps this is a wake up call that time and protocol changes do not stop when Microsoft support does.