Hi there, JoelKirsch.
I see that there are a few emails you simply can't delete from your Outlook account using the Mail application on your iPhone. When you delete them, they reappear shortly afterwards, and I'm glad to help.
How to delete emails on your iPhone, iPad, and iPod touch -- This article provides the information and steps that you need under "Edit mailbox settings". Make sure that the Deleted Mailbox setting is set to Trash. See if those emails can be completely deleted.
Change common iPhone settings -- Go to Settings > Passwords & Accounts, and turn off Mail for the account. Then restart your iPhone Restart your iPhone, iPad, or iPod touch. Once your phone is back to the Home screen turn on Mail in the account again and see if those emails are gone. If you’re using more than one email account, test each account in turn.
Add an email account to your iPhone, iPad, or iPod touch -- If the emails are still present, go to Settings > Passwords & Account. Tap the email account you're having the issue with, and tap "Delete Account" at the bottom of the next screen. Then restart your iPhone again. Once you're back to the Home screen this time, re-add the account and test.
Delete built-in Apple apps on your iOS 12, iOS 13, or iPadOS device or Apple Watch -- If the issue persists, delete and restore the Mail application and test once more.
Let me know how that goes, and take care!
