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.

Roger in Vancouver Not Registered
Posted: September 23, 2007 at 4:05 AM EST
FINALLY a solution to this annoying problem – HUGE thanks to all the fine folks at BERRYREVIEW.com! Keep up the great work.
BerryReview ( View Profile) Senior admin - Posts: 5298
Posted: September 23, 2007 at 11:05 PM EST
Glad we could help Roger! Let me know if there is anything else
slamgauge Not Registered
Posted: September 14, 2008 at 4:17 PM EST
So I set up the filter and I still get dup email. I followed the procedure step by step.
Shelbs Not Registered
Posted: September 17, 2008 at 9:15 AM EST
I also followed the step by step directions and I am still getting duplicate emails….it’s really annoying, there should be a way to fix this.
AJ Not Registered
Posted: December 23, 2008 at 5:01 PM EST
This isn’t really the best workaround. I often send myself emails with information for quick access and this workaround would prevent this helpful practice, no?
James Not Registered
Posted: January 8, 2009 at 2:41 PM EST
I feel the same way AJ. I send myself emails all the time. I’m frustrated BBerry doesn’t have more robust filters that would allow me to do something like “Filter all EXCEPT [subject: note to self]” for example. Anyone have any thoughts?