Well if you thought that deleting emails on the iPhone meant you were deleting emails you were wrong. A new security bug has revealed that when you delete emails on the iPhone it doesn't delete them, it just makes them slightly harder to read.
Delete your email. Remove it from trash. Check the mail server to confirm that the email is gone.
Go to Spotlight on your iPhone and search for the subject line of the deleted email.
Try to open your deleted email that appears in the Spotlight search results. Your phone will crash.
Try again. You'll be surprised to find that your deleted email opens fine.
While this is known to affect POP email accounts on the iPhone it is unclear whether or not it happens with IMAP accounts. Many reports say it does while many others say it doesn't -- probably depends on what IMAP email service you are using.
Apple is aware of the bug and says that the fix will come in firmware 3.1