@BigBoy7: Please can you confirm what the error message says, and at what point you receive it? In the meantime, please 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 > Scroll down to Outgoing Server > Security type > None. I also recommend signing in to your account via your email providers homepage, to see if the issue persists.
I'm having the same issue. With 2 Samsung phones and tablet. The emails will send on other devices that aren't using the Samsung mail app. I have most recent update, but continue to get undelivered mail messages. Very frustrating when running a business.