OE? So you're using XP? What's the reason for switching to Thunderbird?

In order for us to better investigate this issue you need to add a little more non-personal information.

Please add the troubleshooting information to your post. To find the Troubleshooting information:

• Open Help (or click on three-line-icon and select Help)
• Choose Troubleshooting Information
• Use the button Copy to clipboard to select all. Do not check box "Include account names"!
• Paste this in your post.

Please also add the result of these troubleshooting steps to your post

• Does Thunderbird work in TB Safe mode (see Thunderbird Safe Mode)?
• Do you use anti-virus and firewall software? What is the version?
• Who is the email provider?
• Who is the internet provider?
• What is the exact error message?
• What steps did you take right before this happened?

Please post back with this information and any other questions you might have.

Thanks for your suggestions, but...

before I got your reply the problem "fixed itself" - I tried deleting my email account in Thunderbird and creating a new one (which happened pretty much automatically - I didn't need to make any guesses about incoming and outgoing mail server names, server port numbers, etc.). And Thunderbird went right to my email...!

I am currently running XP (and had installed and used Thunderbird in the past) but I'm getting ready to move to Win10 on a different computer. I haven't (yet) switched to Thunderbird, but will when I start using Win10. I will take the XP off-line so won't be able to use it for email.

My efforts to use Thunderbird today on the XP involved experimenting with font sizes for a friend, but then Thunderbird couldn't get to my email.!!