Google Product Forums
Re: Issue with emails disappearing from Gmail online view - though still appearing on my linked Blackberry.
The C Man (Elder Advisor - Mobile Laureate)
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Reading and Receiving Messages
It would help if you said which way you receive Gmail so please use
Blogs: Mobile Gmail Variations
if you are not sure.
If you can find it on your Blackberry then please use Search from your pc with the same subject line.
Would also help if you said which Inbox layout you use.
The New Gmail buttons
would help with this.