FAQ: Duplicate Gmail Emails Being Pushed/Forwarded To Your BlackBerry

RIM has finally conceded the issue with Gmail emails showing duplicates on your BlackBerry and has posted an approved workaround that many people have been using for quite awhile. The problem originates from the fact that Gmail does not have a folder structure and all email including sent mail is stored in the same folder. The solution is more of a workaround where you set a filter on your BIS to not forward messages sent to yourself. Check out the full instructions on this BlackBerry Knowledgebase article.