To diagnose problems with Thunderbird, try one of the following:

• Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender.
• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

Gowpen,

None of the suggestions above solved the problem. I suspect this problem arose after the many Win7 x64 updates that I installed in the past 10 days. There are too many for me to uninstall to find the culprit.

You could try a clean install of Tbird. But first make a safety-copy of your profile.

From Common responses:

Certain Thunderbird problems can be solved by performing a Clean reinstall. This means you remove Thunderbird's program files and then reinstall Thunderbird. Please follow these steps:

1. Download the latest version of Thunderbird from http://www.mozilla.org/en-US/thunderbird/ and save the setup file to your computer.
2. After the download is complete, close all Thunderbird windows (Click Exit/Quit from the menu button on the right).
3. Delete the Thunderbird installation folder, which is located in one of these locations, by default:
   • Windows:
     • C:\Program Files\Mozilla Thunderbird\
     • C:\Program Files (x86)\Mozilla Thunderbird\
   • Mac: Delete Thunderbird from the Applications folder.
   • Linux: If you installed Thunderbird with the distro-based package manager, you should use the same way to uninstall it - see Installing Thunderbird on Linux. If you downloaded and installed the binary package from the Thunderbird Download Page, simply remove the folder thunderbird in your home directory.
4. Now, go ahead and reinstall Thunderbird:
   1. Double-click the downloaded installation file and go through the steps of the installation wizard.
   2. Once the wizard is finished, choose to open Thunderbird after clicking the Finish button.

WARNING: Do not run Thunderbird's uninstaller or use a third party remover as part of this process, because that could permanently delete your Thunderbird data, including but not limited to, extensions, emails, personal settings and saved passwords. These cannot be recovered unless they have been backed up to an external device!

Please report back to see if this helped you!

Thank you.

Gospen,

Will try this tonight (I have a real-time data feed coming into my computer during working hours and cannot interrupt it.) Fortunately I back up my complete T-bird profile directory and subdirectory every night to another physical HD, so that it is easily recoverable. I also back up T'bird once a week usig MozBackup. If memory serves me correctly, a new installation will create a new profile, and at some point I will be asked to select one of the profiles T'bird finds. Is this correct?

A totally new install would create a new profile, but this already has a profile at the right position and will, as it does on updates, use the existing profile. View profile.ini at %appdata%\roaming\thunderbird

(If it doesn't, delete everything inside the new profile and copy everything from inside the old profile here.)

Gnospen,

Reinstalling T'bird last night did not solve the problem, but the reason for it -- and a solution -- popped into my head first thing this morning. I am red-faced at not seeing this days ago, but will explain it in case others become as befuddled over a similar problem.

The addresses I wanted to put into a list came are for 204 members of the community where I live, and were provided to me by another resident who had typed them into her address book. All of the email addresses were in the First Name field, with nothing entered into the email or last name fields. Therefore, when I copied her entries to my list, no email addresses appeared and it could not have been used for a group mailing. I would think that at least the information in the GivenName field would have shown when I dragged and dropped from her list to mine, but they didn't. Still can't figure that out, but I got around the problem by exporting her "address book" to a LDIF file and editing the "given name" label to "mail". Then imported that address book. I then made a new list in my personal address book (which is the arrangement I prefer) and was able to drag/drop all 204 entries en-masse.

The reason I went through all this is that the person who sent out the group mailings and gave me the addresses shows all recipients in the "To:" field. I explained she should send out group mailings using the Bcc: field, in the interest of attempting some degree of privacy (even if Bcc names can be seen if one knows how) , and she didn't know how to do this. Don't know why I didn't see the problem earlier. Thanks for your help.