Is an account remaining that was tied to that email host? Is there more than one account on your Thunderbird and did all messages come through? Click help>moretroubleshootinginformation, scroll down and you will eventually see a table that lists all accounts and their servers. That may show the affected account.

Yes, it appears in the Task List of Troubleshooting Information. How do I cancel this task? There are several email accounts, but not this one. I have other accounts with the same domain, but not the same name@ part.

Type caldav Disabled true Read-only false iMIP Identity id1 Event Supported true Task Supported true Auto-Scheduling Supported false

Okay. Next, click help>moretroubleshootinginformation and scroll down until you see a table of info with title of 'Mail and News Accounts' and see if that account is still listed. If it is, that indicates you have not deleted all components.

The troublesome email address is not listed in 'Mail and News Accounts'. In fact, the @domain is only listed once on the page, under Task List.

Well, I don't use the task feature, so cannot assist there, but at least you now know where the problem lies. Good luck.