After some testing, I have figured out what is going on.

The problem is when you drag and drop several contacts to a mail list, and one or more of those contacts do not have an e-mail address. Thunderbird is not supposed to allow adding contacts to a mail list if there is not e-mail address, but somehow it can happen, and that "messes things up".

See Bug 1298247

Double-click the mail list to open its edit window, then go through the list and delete any contacts that do not have an e-mail address. Then the mail list will show properly in the display.

Why do you have so many people in a mail list? The purpose of a Mail List is to be able to easily send a single e-mail to everyone in the list. If you try to send a single e-mail to too many people, e-mail servers will not allow it. They frown on mass e-mailing because the chances are they will get complaints from some of the recipients. You might be a spammer.

These days, the proper way to send legitimate mass e-mails (like newsletters), is to use an online mail list/newsletter service. They require people to opt in to a mail list so then it can be assured that all the recipients actually want the e-mails.

On the other hand, if you are creating Mail Lists in the Thunderbird Address Book to just organize people, then that is not a good way to do it. The better way is to create separate address books for each group. Then you have more address books than just "Personal Address Book" and "Collected Addresses".

When the Address Book is open, press the ALT or F10 keys to show the menu bar. Then click on File: New: Address Book.

If you want the menu bar to always show, then after showing the menu bar by pressing ALT, right-click the menu bar and select "Menu Bar".

Sorry, Bruce gave a better answer already.

Thanks for the replies. NONE of the contacts I added are missing email addresses. (I double-checked.) I'm creating the mailing list because my ISP will be deactivating my email account because I moved and can no longer use their internet service. I needed a way to notify all my contacts of my new email address, because I won't be able to set up an auto-reply or forwarding from my old address. If there's a better/easier way to accomplish this, please let me know! Thanks.

FBrill said

Thanks for the replies. NONE of the contacts I added are missing email addresses. (I double-checked.)

Perhaps one of the e-mail addresses is malformed, thus not a real e-mail address. Like missing the @ symbol, or missing the .com, or something like that.

I'm creating the mailing list because ... I needed a way to notify all my contacts of my new email address ... If there's a better/easier way to accomplish this, please let me know! Thanks.

To keep your e-mails from being labeled as spam, I recommend sending that e-mail to no more than 10 recipients at a time, and wait a minute or two before sending each e-mail. You can save the e-mail as a template, instead of a draft. Then you can open the template for each e-mail.

Using mail lists would be superfluous in this case. If you press F9 while the Write window is open, it will show you your address books on the left side. You can select multiple addresses, then click on "Add to Bcc".

I say to use Bcc, because it is probably not a good idea for everyone to see everyone else's e-mail addresses, so send them TO yourself, and put the other's e-mail addresses in the BCC.

F9!!!! OMG, wish I had known about this a million times before. I've been so frustrated thinking there was no way to view & select address book entries from within a new email I'm writing. Thanks, Bruce! That's all I needed. Awesome.

PS - So sorry for delayed response. Had a couple crises to deal with.