Malicious email or virus, Thunderbird hangs on can't write or not enough disk space

In Thunderbird 151.0.1 [64 bit] I get the following error message: Error Inbox - inbox on .....[my email address] "There is not enough disk space to download new messages. Try deleting old mail, emptying the trash folder and compacting your mail folders and then try again." I did all of that, even went into windows disk cleanup to free up more disk space. I get the same error message. I have 3 email accounts in Thunderbird, only one account has this problem. When I use Outlook express I do not get any error messages but I do get a malicious email that AVG intercepts. So how can I purge bad email from Thunderbird ? Or what else may be going on and what else could I try ? I have deleted all old emails, in Thunderbird, I routinely delete old emails. Thanks alot Sam