Error message when trying to delete a message from iPad or iPhone:
Navigate to your email account's settings
- Go To Settings (Gear icon).
- iOS 9 and earlier: Tap Mail, Contacts, Calendars.
- iOS 10: Tap Mail.
- iOS 11: Tap Accounts and Passwords.
- Select your email account.
- Tap the "Account" line to pull up the settings sheet.
- Scroll to the bottom of the page and tap Advanced (At the very bottom. You may need to hide the keyboard to see this.)
Set up Mailbox Behaviors to store message in the correct folders "On The Server"
- Under the "Mailbox Behaviors" section, select "Drafts Mailbox"
- In the new window, select the "Drafts" folder from the "On the Server" section. You should see a check mark next to this folder. Do NOT check the "On My iPhone" "Drafts" selection at the top.
- Tap the "Advanced" button on the top left to go back to the advanced page.
- Repeat this process for the "Deleted Mailbox" and "Sent Mailbox", selecting the corresponding "On The Server" mailboxes. With Gmail accounts, you will also have the ability to map an "Archive Mailbox", which can be linked to the "All Mail" mailbox.
- Tap the "Advanced" button on the top left.
- Tap on "Account Info".
- Tap "DONE" (do not tap Cancel).
You may need to then completely shut down, and then turn your iPhone back on.