I was able to delete 6 of those.
The last has hidden itself in a .dll file, and refuses to be deleted, even after changing its write protect and everything.
So, I simply changed the name of the file (it let me do that!), and all I can hope for is that nothing will try to start it as it is now. It still won't let me delete it! :(
I've also gone in to my address book and deleted all the accounts of whom I don't remember the owner, and all the dump accounts (or whatever they're called -- the ones which send out bulk mail) which I never put in there in the first place.
Hopefully, I won't get anymore bounced e-mails which I never actually wrote.
To those of you who got hit by me... sorry 'bout that. Should be fixed.