Dunno if your problem has already been solved but today I encountered the same issue after fiddling around with some custom lockinfo icons and several resprings.
There were five mails that always showed up no matter what I did. Man, I even deleted both my mail accounts with no success. Then I did some searching in iFile and finally discovered a suspect:
'com.ashman.lockinfo.MailPlugin.cache.plist' located in '/var/mobile/Library/Caches'.
I backed it up and deleted it, then set up my mail accounts again, enabled lockinfo's mail plugin and voila - no more deleted mails displayed in lockinfo!