This has been reported as Bug #1060901. If you have an account on Bugzilla, please consider voting for that issue.

Several other people have sent in the same support request as you, noting this happened after they upgraded to version 31.1.

The exact error message is: XXXX is not a valid e-mail address because it is not of the form user@host. You must correct it before sending the e-mail.

This happens in Thunderbird 31.1.0 when your mailing list description includes several words separated by spaces.

Although not ideal, these workarounds should let you use your mailing lists until a proper fix is implemented:

• While composing an email open the address book and select the list you are trying to send to, highlight all the names in the list and drag them to the To: box. This uses your existing data without modifying it.

• Replacing the blanks " " between the words in such lists' descriptions with an underscore "_". This requires modifying your mailing list(s) description(s).

About automatic updates

Automatic updates are the default in Windows.

You can customize such behavior, however, it's under Tools > Options > Advanced > Update.

My suggestion would be to set it to Check for updates, but let me choose wether to install them., specially if you depend on email for critical / important business or personal matters.

I'm wondering if I reinstall TB30, or any other earlier version, if that solves the problem.

The newer and better Tbird may be newer . . .but it ain't better.

Pain in the fanny pack.

Well, this problem is specific to 31.1 so installing any previous version will avoid it. The workaround is fairly easy, though.

In Windows Thunderbird updates are automatic by default. To avoid similar situations in the future, you could change that and decide to have a more conservative approach to upgrades.

Before trying anything, make a backup of your current Thunderbird profile.

You can uninstall the current Thunderbird version via Control Panel > Programs and Features and reinstall a previous version, download it from here:

• Version 31.0
• Version 24.8

Click on the type for your OS. eg: If using Windows select 'win32' then select the language eg: en-GB = English british then download the .exe file

You can customize automatic updates behavior, however, it's under Tools > Options > Advanced > Update.

My suggestion would be to set it to Check for updates, but let me choose wether to install them., specially if you depend on email for critical / important business or personal matters.