With iOS, Mail archives Gmail messages on iPhone, iPad, and iPod touch. Archiving messages allows you to store messages you're done with but don't want to delete.
When you archive a message, it moves to the All Mail folder. Mail doesn't delete the message from the Gmail account. Using the Archive setting replaces all delete options, including tapping the Trash icon while you view a message, and selecting Edit to manage multiple messages.
To turn off Archive, go to Settings > Mail, Contacts, Calendars > Gmail Account > Account > Advanced > Move Discarded Messages Into.
Learn more about the Gmail archive feature in Gmail Help.
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