If you have a blackberry and you have your personal e-mail forwarded to it (not your corporate mail) when you upgrade it, send it in for replacement, or even just toss it away, you MUST remember to log in to the BIS server at bell.blackberry.net or telus.blackberry.net or rogers.blackberry.net ... depending on who your phone company is, or just through the mail setup icon on the blackberry device, and disable the forwarding. This does not happen automatically when you cancel your phone plan or move it to a new phone.
The corporate mail is different, it comes through a corporate BES server hosted at your company, and they can easily shut off the forwarding of any info to the blackberry device, but BIS used for personal e-mail is managed via the blackberry.net servers and linked to an account that only you know the password to. It collects the mail and forwards it to the device you specified by PIN #, which is attached to the device, NOT your account!
If that device is reused by another user with another phone #, the BIS server will still send your mail to the device until you log in and tell it not to.
That is just one more reason I dislike the BIS setup rather than letting the blackberry connect directly to the POP/IMAP server for personal e-mails. #1 I don't like that I have to trust RIM and their partners with my personal account passwords, and #2 wiping the blackberry and cancelling the phone plan isn't enough to ensure that the next guy doesn't get free access to my mail. I also have to either log in to the BIS and cancel forwarding, or change my e-mail password.This is also why I discourage the use of PIN messaging except as an alternate, emergency communication channel if normal e-mail is down.
People still think of PIN as being more private than e-mail, but it is not. It can be, and often is, logged at one or both end's corporate servers, but if your contacts have an old PIN# in their address books and they try to PIN you a message, but somone else owns that Blackberry device now, guess who gets the message!