I am not sure understand your problem, but if an account is not appearing in unified folder, try this:

1. highlight a unified folder,
2. rightclick and select 'properties'
3. then, select 'choose' and place tick mark by desired account folder.

Tx, David, but the problem (not fixed by your advice) in trying your recommended steps, is that properties does NOT give/have a choose (button) choice. So, there is no "desired acct folder" (step 3 above). Repairing inboxes did not help. It's a folder pane prob. But thanks for trying.

Just in case it's not clear enough: in unified view, there is an "inbox."

Contained in that single "inbox" are listed all the email acct names, for example listing a bogus set:

Inbox

 testbox@testbox.com
 testbox2@googlymail.moc
 andsoforth@etc.zzz

A 4th acct exists, we'll call it

 boxtest4@4box.ten

This 4th acct is NOT present in the unified view.

So all 3 under unified inbox are separate accts, which appear in their places way down the folder pane column separately, using the "All" view choice, as inboxes and with the word "inbox" there under acct name. So does "boxtest4" acct, in the All view.

So, in "unified" view, folder pane shows the word "inbox" just once at top of folder pane, and all the inboxes of each acct are not "called" inboxes, only their acct names are listed (for example as above, "testbox@testbox.com").

I don't know why boxtest4 acct isn't present in "unified" view [that is, the mail in "inbox" for boxtest4 acct. isn't present in the unified inbox]. That's the problem. Thanks.

I need to further clarify: in "Unified" folder view, the "inboxes" are NOT listed below, with some acct folders in the folder pane (like "known spam" "sent spam") . The inboxes are all, only, in the "master" inbox at top of folder pane. Except for "boxtest4", where the inbox acts as if it is the "all" view for folder pane, it does not unify with all the other email acct inboxes at the top of the folder pane, in "unified" view.

Absent solutions here, I guess I can try just deleting the acct from t-bird and re-entering it as a "new" acct. Is there hidden code which would prevent success if I try that? Config ed to fix? I don't code. Tx.

What do you see when you highlight and rightclick the unified Inbox folder? If 'properties' is an option could you do a screenshot of the properties pane? This could be a bug. Thank you.

Hi, thanks, here you are. -What's your experience on doing what I plan, rather than wait for possible fix, if any -- just backup tbird accts, delete the problem acct & add it as if new? Note the acct again is the MS "outlook365" outlook.office365.com. Tx.

Note the 'choose' button on right side of your screenshot. That is the button I suggested in original response. Click it and you should see options on what accounts to include.

Thanks! Duh?! Why didn't I see this before? The outlook inbox was unchecked. Now checked, its inbox is in its place in unified. Saved me from asking which profile in w11 I should save, local or roaming, if I had to back up before r & r outlook profile. Thanks again!

I was glad to assist :)