What version of Thunderbird? What is your platform? (Windows, OSX, Linux…) Who is your ISP? Who is your email provider?

Or it may be simpler just to post your troubleshooting information.

To find the Troubleshooting information:

• Open Help (or click on three-line-icon and select Help).
• Choose Troubleshooting Information.
• Clear the check box Include account names.
• Use the button Copy to clipboard to select all.
• Paste this in your reply to this message to this forum.

Name: Thunderbird

   Version: 52.6.0
   Windows 8.1

   account1:
     INCOMING: account1, , (pop3) pop.ntlworld.com:995, SSL, passwordCleartext
     OUTGOING: , smtp.ntlworld.com:465, SSL, passwordCleartext, true

Does it make any difference if you use the recommended settings, i.e. smtp.virginmedia.com on port 465, SSL/TLS security, authentication = normal password, User name = email address.

Do you have an antivirus program scanning outgoing mail or monitoring email connections?

Thank you!

• I don't see anywhere to enter an smtp server name, only a pop name - if I enter the smtp name there is no connection at all, nor is there on "pop.virginmedia.com"
• Port 465 doesn't connect at all
• I have tried turning AV scanner off, doesn't help

Open Account Settings.

The last "account" in the list of your accounts is where you'll find all your existing SMTP settings bundled together.

The correct incoming POP server is pop3.virginmedia.com on port 995, SSL/TLS security, authentication = normal password, User name = email address. Outgoing server settings are found as noted above.

Thanks guys, changing the smtp server name seems to have resolved this. Thanks so much.