Open the Mail app on your iPhone
Go to the mailbox or inbox with the emails you want to delete
Swipe left on an email
Tap Delete
To delete multiple emails, tap Edit
Select the emails you want to remove
Tap Delete or the trash icon
To delete all emails in a folder, tap Edit
Tap Select All if available
Tap Delete
To permanently remove deleted emails, open the Trash folder
Tap Edit
Select the emails or tap Delete All if available
Confirm the deletion if prompted