According to the Gmail blog’s tip “Archive mail on your iPhone” by default the iPhone will delete your Gmail, which will be deleted in 30 days from your Gmail forever. Since Gmail is big on archiving they’ve written this tip to help you avoid losing your valuable email:

First, get rid of your default set up. Go to Settings > Mail, Contacts, Calendar. Find your Gmail account under “Accounts,” click on it, scroll to the bottom, and click “Delete Account.” Don’t worry — it’ll be back and better than ever in a sec.

Then manually configure IMAP using the “Other” menu option…

The tip above concludes by either watching a YouTube video (below from the original post) or visiting the Gmail Help Center here.

GMAIL/IPHONE VIDEO ON YOUTUBE
YouTube Preview Image

For more info and options check out the original Gmail post here.