Send Receive Error - Time Warner Internet

This question is about "Send Receive Error", with Time Warner Cable internet and apps. Outlook 2019 (packaged with Office 2019); Windows 10 Professional with latest update

Starting on 1/30/19 I have been getting a send receive error with this message

Task ' - Sending' reported error (0x800CCC0F) : 'The connection to the server was interrupted. If this problem continues, contact your server administrator or Internet service provider (ISP). The server responded: 550 5.1.0 ESMTP server not available AUP#O-1070'

I have been receiving messages from various senders with no errors. My wife’s computer has no errors. She has an earlier version of Outlook and Windows 10 Professional. We both have Spectrum as our ISP.

I have done the following:

· Reset the cable modem

· Reset the Wi-Fi modem (wife’s computer uses Wi-Fi, mine uses direct cable)

· Checked IMAP account settings; they are exactly the same as they were before the error

· Sent test message to my computer--message received

· Sent test message to wife’s computer—message received

· Wife sent message to my computer-- message received

· Looked at Spectrum server email and it looked normal

· In desperation, reinstalled Office 2019—error persists

I am baffled by this error, and would appreciate your help.

Send Receive Error?