Where does the Gmail data reside?

I imagine it probably either hangs in googles cloud or goes onto your sd card.

 

Actually all it does is push the "TEXT" portion of the email to you. In order to get the attachments/embedded pictures you would still have be online to download it and save to SD card.

 

The data is stored on your sdcard, since it's accessible offline. As FrogSplatter said, it only downloads the text, not attachments. The other reason it won't take up much space is because it only downloads a subset of your mail. If you go to the Gmail app, then -> Settings -> Labels, by default (on my Spica anyway) it's only set up to sync Inbox and Sent from the last 4 days. I don't know what would happen if you turn that up to something that did have to download more data than you have space for, but without attachments, you would have to have a huge amount of emails in a short space of time to even get as high as 10MB, never mind 228MB

 

Hmm, my Number of Days selection seems to be working fine atm, but I only recently changed that up to 30, so maybe the older ones will stay. You haven't set some of the individual label options to "sync all" by any chance?

 

I asked Motorola this question before I bought the Droid. Email (at least in the default Gmail app) that is synced to the Droid is stored in main memory (the 256MB that is shared with applications). Currently they do not have an option to store email on the SDCard and they wouldn't say if/when that option might become available.

Their recommendation was to use the number of days to sync setting (already mentioned above) to manage how much data is synced to the phone.

It does appear that attachments are NOT synchronized -- it goes to the gmail server when you tap the preview button.

Also, you CAN access email that isn't synced to the phone. When you try to scroll to any message summary beyond what is already stored on the phone, it will briefly display a message that it is getting the additional information. After that you can view those emails (it seems to directly load them as needed from the server without actually storing them with the synchronized messages). The way it works seems fairly smooth and intuitive -- I have to complement google on that.