How Offline Gmail Decides Which Messages to Download
When you enable Offline Gmail, the new service doesn't actually download all your messages—just about 10,000 of them. And Gmail has its own method of determining which messages it stores for serious email fiends.
Todd Jackson, Gmail's product manager, gave CNET's Webware that 10,000 email figure. And Googlers who work on Gmail posted the same 10K estimate, while offering an explanation of their "heuristic" algorithm that tries "not to download uninteresting conversations."
The short version: Offline Gmail estimates a time span that covers about 10,000 messages and almost all of that period. It definitely syncs any label that's not too huge, was recently updated, and has some history, including the nearly-guaranteed Starred and Drafts sections. It skips un-labeled Trash and all the Spam, and any label that's mostly unread.
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