I understand your plight! I've forwarded an email on my iPad accidentally to my x-wife by typing in the first two characters to an email address I owned. The apple software developers didn't think about the user needing to clean up the email cache bucket. Thanks Apple. I wouldn't have made that simple programming error at Boeing! I've been staring at that old address for a year trying not to select it when forwarding mail to one of my other accounts. The addreses start out with the first 3 characters being the same. I'm always fat figuring it. I wonder if you could sue Apple if you accidentally forwarded sensitive information to an unintended party. Probably not, but maybe they will get paranoid and do something to fix this feature.
Apparently for the problem I was having. Looks like they are cleaning up the contact list buffer as you delete them. I was getting old email addresses I had deleted along time ago in my suggestion list of email addressees as I entered one or two characters in the email to field. Nice to be able to see a suggestion list of current addresses in your contact list but not the ones I deleted.