Is this definitely nothing to do with your email server @mike51t ?
Check the accounts added to your phone and double check the sync settings.
🌈 Stay Safe & Stay Alert. 🌈
Current Phone > Samsung Z Fold³ 5G.
@mike51t: Can you try opening the Email app > Tap the 3 lines in the top left > Tap the cog in the top right of the pop up window > Select your account > Scroll down to Server Settings > Incoming Server > Delete Email from server > Change this to 'When deleted from inbox'. This will allow you to permanently delete emails from your inbox via your S10.