Help Gmail: How does the "Sync Messages" setting work?

[JohnJSal]

[Apologies if this isn't an appropriate place for this post. I tried the Android Applications forum, but it's been days with no response!]

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I just can't figure this out. When you go into the settings and set the "Sync Messages" option to either None, Last XX days, or All, what happens with each option?

I would think syncing All would simply sync everything on your Gmail account with the app, but this isn't what happens when I choose it. It only seems to sync some of my mail. However, if I set it for Last 30 days, it doesn't just sync the last 30 days of mail, but it seems to sync everything! Or at least much further back than the past month.

Please, someone explain how this setting works!

Thanks.

Edit: I just noticed for some of my labels, it is set to not sync at all, yet when I go to those labels, everything is there! What's going on!?

 

[Szadzik]

All is all and syncs messages IN THAT SPECIFIC FOLDER, not in all labels. Each label hasa setting for syncing.