I am using the Daily version an all I need to do is click to edit the mailing list, and then enter first few letters of a name and all email addresses for the individual appear, eligible to be added to addressbook.

Yup, I've done that, and it initially appears to work (the newly-added address appears in the list). But after clicking the OK button to end the editing of the list, then again editing the list to verify the change, the newly-added address isn't there, only the default address.

A little more info/details/notes about my problem, after some testing, etc. ....

First, I'm on a desktop running Windows 10, using Thunderbird 128.10.0 from the esr update channel, which is the current version according to "About Thunderbird."

- John Doe is in my Address Book, and has two email addresses, with one marked as the default. John is also in my "Nice People" mailing list, using his default address. John would like messages sent to the mailing list to go to both of his addresses.

- Editing the "Nice People" list and adding a new entry for John Doe using his non-default email address appears initially to work, in that he appears in the list twice, once with each email address. But after clicking the OK button to end the editing of the list, then again editing the list to verify the change, his new entry with the non-default address is gone.

- As a test, I deleted John Doe from the "Nice People" mailing list. Then I edited the list and added him back, but using his non-default address, and clicked OK to end the editing of the list. Re-editing the list shows that John is there, but with his default address, not the non-default address I specified when I added him to the list.

- I wondered if having a default email address was required. Apparently it is. I edited John Doe's Address Book entry, unchecked the "Default" box so no address is marked as the default, and click "Save." But re-editing John's Address Book entry shows the "Default" box for his first email address has automatically been checked.

- In summary, it appears that mailing lists in Thunderbird always use a person's one and only default email address. The only way I've found to send copies of a "Nice People" mailing list message to both of John Doe's email addresses is to create two entries for him in my Address Book, one for each email address, and add both entries to the list.

- If someone knows a better way, or if there's some setting that's causing this problem, I'd love to learn about it.

I can reproduce this problem. I located a bug report on the issue: https://bugzilla.mozilla.org/show_bug.cgi?id=1799356

Has any work been done on fixing this problem since I reported it five months ago? I'm now using 140.3.1esr, and the problem is still there.

With the current government shutdown, I now have an even more important need to be able to send email to a group of about 50 people using their home email addresses (currently listed as their non-default address), rather than their work addresses (currently listed as their default address). To do that, I now have to either (1) edit each person's entry in my address book to change their default email address (then change them all back once the shutdown is over), or (2) create a second entry in my address book for each of those people, with their home address as the default, and then create a new mailing list with those addresses.

What I'd really like to do is to have one mailing list, with the ability to include both default and non-default addresses for people, as described in my original query back in May.

To clarify, what you describe is not a 'problem' except to you. The developers receive many suggestions, but that does not mean they accept them and, even when they do, it might be years before some suggestions are implemented.

I'd be willing to bet that I'm not the only Thunderbird user who's had this "problem." And as a software developer in my prior life, I certainly understand that not every issue can be fixed immediately. Especially for free software like Thunderbird. I wasn't really trying to be critical, just asking about the status.

As an earlier response by Toad-Hall noted, this issue was reported as a bug (Bug 1799356).

I've now just looked more carefully at the bug list (which I should have done before asking, my fault), and see that it was reported by Thomas D. three years ago, is classed as a serious (Severity S2) defect, listed as NEW, and hasn't been assigned. And, the same issue was reported 14 years ago (Bug 694925), which was closed when 1799356 was created. In one of the comments in the discussion of Bug 694925, it's noted that due to how mailing lists are implemented in Thunderbird, "there is probably no reasonable 'fix' for this bug."

So at this point I'll go ahead and created a second entry in my address book for everyone this involves, with their home address checked as the default, which will allow me to add both their work and home address to a mailing list.

One other comment, FWIW. As it currently stands, when a user attempts to add a non-default email address to a mailing list it appears to work, but Thunderbird actually silently adds the default address instead. Unless the user later checks the list, they may not catch that. It'd be nice if some kind of warning/error message was presented to the user when they attempt to add a non-default email address to a mailing list saying you can't do that.

Has any work been done on fixing this problem since I reported it five months ago? I'm now using 140.3.1esr, and the problem is still there.

Did you click the link to the relevant bug. Toad-Hall posted it https://bugzilla.mozilla.org/show_bug.cgi?id=1799356 where you can appraise yourself of all the discussion and work that has occurred since your last visit.

Matt - yes (but I should have done that earlier). See my post from yesterday, just above yours.