How to Delete Gmail Email on iPhone
By default, your Gmail inbox on the iPhone works a little differently than e.g. your iCloud email. Rather than truly deleting messages, Gmail will offer an “archive” button that moves your email to a special archive folder while keeping it searchable. This might be of use for some, while other prefer to actually delete their gmail emails on iPhone instead of archiving them. Here’s a guide on how to delete gmail messages.
There are two ways to (irreversibly) get rid of a Gmail message. The first method is available on-the-fly and allows you to selectively trash an individual message, while keeping the default of archiving old email. The second method changes this default setting to trashing all messages you wish to remove.
Deleting a single gmail message instead of archiving it
Open up the message in question in your Gmail inbox on the iPhone. At the bottom of your “Mail” app, you should see a tiny icon representing a box with a lid on.
Tap and hold the “Archive” button’s icon as opposed to simply tapping it. A context menu should show up, offering the choice between archiving and deleting the mail. Tap “Trash Message” to delete the email. The message will then be placed in the trash folder, which then empties itself after some time. Your message is now truly gone!
Changing the default from “archive” to “trash”
If you prefer to trash all of your email instead of archiving it in your Gmail account, you can change the default setting in your iPhone’s “Settings” app. To always delete your discarded gmail messages, go to “Mail, Contacts & Calendars” in your settings panel. Select your Gmail account from the list, then tap it’s name in the next screen and finally select “Advanced” to get to the relevant settings page.
Look for the section titled “Move discarded messages into:” and select “Deleted Mailbox” as opposed to the default of “Archive Mailbox”.