Problem - Thunderbird Gmail Norton

[SueDonim]

I reinstalled Norton. I've left the scanning for email attachments turned on but the certificate problem is still there. I've let it through again but this time didn't tick the "permanent" box and clearly need to do something better. I'll look at reviews etc and consider Eset. I've just run a free Malwarebytes scan which was clear. I'm not sure that I would trust Defender enough on its own. I keep Windows as updated as it will but this computer is getting a bit old now (?2017) and I sometimes get messages about compatibility, although they are mainly telling me that it can't do Windows 11.

Thanks very much for your help.