In settings, at bottom, neither about or advanced had anything to help.
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In settings, at bottom, neither about or advanced had anything to help.
I think this may be what you're asking about. If not, please clarify your question.
For an IMAP account (such as Gmail):
On OS 10.2.1, you have to select the sync period option when setting up the account -- so you'd have to delete and re-add it. Use the standard email setup, until you get to the screen that gives you the option to toggle on/off contact/calendar sync. Tap "Advanced" at the bottom. Scroll to the very bottom, and set the "Initial Retrieval amount" to "Forever" (or your preferred sync period). You can also set your sync interval here as well.
On OS 10.3.x, you can now change the email synced to your device. Go to Settings > Accounts. Scroll down and select from the drop-down "Sync Timeframe".
Note that if you'll be syncing a lot of messages, you should be on WiFi, unless you have a very generous data plan.