Who is the mail provider, and what are your settings? An example of what could be happening is that the new computer has an AT&T-type account that requires a separate secure mail key for each computer.

Here are our server settings:

Secure SSL/TLS Settings Username: [email protected] Password: Use the email account’s password. Incoming Server: scottshearings.com

   IMAP Port: 993
   POP3 Port: 995

Outgoing Server: scottshearings.com

   SMTP Port: 465

Authentication is required for IMAP, POP3, and SMTP.

Non-SSL Settings Username: [email protected] Password: Use the email account’s password. Incoming Server: mail.scottshearings.com

   IMAP Port: 143
   POP3 Port: 110

Outgoing Server: mail.scottshearings.com

   SMTP Port: 2525

Authentication is required for IMAP, POP3, and SMTP.

Your settings for secure connections look OK, according to the siteground site, but it looks like the server for non-secure should be the same, i.e. your domain, without mail. at the beginning. They also indicate how to find the server hostname.

Are you using secure or non-secure settings, and how are the other computers set up?

Ok thank you :) We are trying to use the secure settings and the other computers are using the secure settings too. Should we be trying to use the non-secure settings instead or?

Check to see if Thunderbird has access to the internet. Q: Does your Firewall have Thunderbird listed as an allowed program?

Q: What have you got set up in proxy settings: Menu app icon > Preferences > General 'Network & Disk Space' section Connection....click on 'Settings'

compare setting with other computers.

Suggest you use: Incoming Server: scottshearings.com IMAP Port: 993 Connection Security: SSL/TLS Authentication Method: Normal Password Username: [email protected] Password: Use the email account’s password.

Outgoing Server: scottshearings.com SMTP Port: 465 Connection Security: SSL/TLS Authentication Method: Normal Password Username: [email protected] Password: Use the email account’s password.

Hi thank you for your help but unfortunately it is still coming up with the same error. Thunderbird was not listed on the firewall at all - but I have added the programme now and it is still not logging in. I also checked the proxy settings and it is the same as the other computers which is 'use system proxy settings'. Is there anything else that could be stopping me from logging in?

Look for interference from some external app like a VPN or antivirus. If you run Windows in safe mode to bypass startup apps, that will test their effect. In general, the TB profile folder should be excluded from antivirus scanning (leaving the real-time background scan in place). Computers with the same mail settings but different AV apps can result in different outcomes.

This has just happened to me...again. I am now done with Thunderbird. It is not fit for purpose.

This sounds like you have a program on that computer which is running a VPN. Do you use Norton ? What Anti-Virus are you using? You mention 'new computer' is it running Windows 11 ?