What is your anti-virus software?

I am using MalwareBytes.

Thanks.

Try to start Windows 10 in safe mode with networking enabled.

Does the problem go away?

Windows safe mode disables anti-virus software. This is a troubleshooting step, not a solution.

Thank you for helping me. In Safe Mode with Networking the same error message results: "Sending of the message failed. The message could not be sent because the connection to Outgoing server (SMTP) mail.twc.com was lost in the middle of the transaction. Try again." I am able to receive messages. Also, I am able to send and receive messages using Outlook. This error suddenly started happening about 3 weeks ago. The same day the problem started I called Spectrum to report it. The technician told me she had received multiple calls that were similar to mine. After troubleshooting over several days, Spectrum concluded that they would not escalate my problem because their platform was working. Thanks again for your help. I appreciate it.

Have you compared your setting in outgoing server (SMTP) to those on the spectrum web site here https://www.roadrunneremail-login.com/blog/roadrunner-email-pop-server-settings/

I checked the settings both on my own and with the help of a Spectrum technician. The settings are correct and are the same as before the problem started as well as being the same as the Outlook client - server setup using a different email address, where there is no problem. Thanks so much for helping me.

You say " I have checked settings and they are correct."

So I'm asuming you have this set up:

• Outgoing server name: mail.twc.com
• port 587
• Connection security = None
• authentication = password, transmitted insecurely
• User name = full email address.

OR are you using same as above with two modifications:

• Connection security = STARTTLS
• authentication Method = normal password

Please note the 'User Name' does need to be the same email address as used for the pop account.

But, I'm not sure what your Outgoing Server (SMTP) settings have been set up to use.

Please post some information showing exactly what you are using to stop all the guessing OR change your settings to what I've mentioned above, then exit Thunderbird, wait a short while and then start Thunderbird.

• Menu > Help > More TRoubleshooting Information
• Scroll to 'Mail and News Accounts'
• Copy all the data and post it into this forum.

• Access 'Account Settings'
• In left pane scroll to bottom
• click on 'Outgoing Server SMTP
• select the smtp in the list
• post an image showing the settings

Did you recently Logon to the webmail account and change your password?

If yes, did you update the stored password in Thunderbird ?

• Menu icon > Settings > Privacy & Security
• Scroll to Passwords section
• click on 'Saved Passwords
• click on 'Show Passwords'

You will have two lines for the account.

1. one is mailbox:// server name
2. one is smtp://server name

• Right click on the smtp line and select 'Edit Password'
• completely remove all contents and then carefully type in the correct password
• click on 'Close'

Exit Thunderbird, wait a few moments and then start Thunderbird to ensure it is using the correct data.