Since app update on 9 April have been getting error and not being able to download emails on Thunderbird. See attached image.
Have been told that Nortons is likely blocking things.
How do I fix it please.
First, no antiviral software can, nor will it, create a MITM attack. They are designed to "protect against" those attacks, Norton will log and alert you if a MITM attempt is detected. MITM DOES, create issues as outlined in the below OWASP site reference. Often they use a wireless access point to gain access and begin their obfuscation. As I previously stated there is an "unsafe" certificate being offered in your screenshot that has nothing to do with Norton in any manner, Norton may be alerting you to it. Does that popup originate from Norton or Thunderbird?
You also posted that you have 2 e-mail addresses/account that lead me to the point that, your internet service is possibly being tampered with. Specifically, your router / provider provided device. Meaning the attack is at the provider level and not being detected or, within your router and again, not being detected by your provider/e-mail provider. The more likely scenario is as stated concerning the illegitimate certificate attempting to be installed.
https://owasp.org/www-community/attacks/Manipulator-in-the-middle_attack
Also, is your version of Thunderbird is older than version 115.7 it is vulnerable under this CVE:
https://www.mozilla.org/en-US/security/advisories/mfsa2024-04/
SA
I should add that I use two email addresses and the same thing is happening with both, so not an email server problem.
I have been back to my email provider and they say it is not their problem, saying it definitely looks like a MITM attack by antivirus software, in this case Norton.
Their certificates are all legitimate.
It has only been happening since Norton did an app update that I was notified about by email on 8 April.
Please provide a solution. It is getting annoying.
Hello Ian. Please look at your screenshot for your answer. In it, there is a security certificate that is being presented for download when your e-mail is trying to authenticate. The statement "Legitimate banks, stores and other public sites will not ask you to do this". Contact your e-mail provider because this is something that is being presented to you from their servers, its not Norton.
Edited: May be related? https://support.mozilla.org/en-US/questions/1259049
SA
I am still waiting for someone from Nortons to assist with the problem I have. It has basically locked up my email through Thunderbird, both send and receive.
Surely someone knows what is likely to be causing it and how to fix it.