Mail Activity Window shows activity on defunct accounts

I just opened the Activity window on the Mail.app, and discovered that in addition to my existing accounts, it was trying to log into 3 defunct accounts! They're not listed as accounts under preferences anymore (one is over 10 years old), but somehow the program is looking for them. If I can't see them under the Accounts pref, how do I get rid of them?

Only other thought is that I do have old mail saved in Mail folders from the old accounts, for reference.

Thanks!