The crash only happened once and I'm happy to post the log, but this does not seem to be the problem here. After pulling off a fair bit of hairs, it seems that a correct explanation of the problem is the following (I started from a fresh empty profile).

I have 2 accounts, from the same mail provider (LaPoste) with no difference, they both don't have any personal folder. That provider has that unusual folder organization where everything is under INBOX and their folder for sent email is INBOX/OUTBOX (I know...), drafts are under INBOX/DRAFT and junk under INBOX/QUARANTAINE

When I add account n°1, TB detects that it should place a copy of sent email in INBOX/OUTBOX and same for draft and junk (although for junk, it does not automatically activate "Move new junk..." but the selected grayed out option is other, "INBOX/QUARANTAINE". In account settings, the "Place a copy in" would show "No available" folder under option ""Sent" Folder on:" is active with and correctly displays "OUTBOX". When I go under the " all folders" view, the INBOX/OUTBOX correctly as the green flying envelope icon.

When I add account n°1, TB does not do any of that detection and wants to create Sent, Drafts and Junk folders. Well, no big deal, I could change that manually although it is *super* weird why it would work in one case and not the other. Again, same provider, fresh profile, no difference I can think of.

Now, the real problem seems to be with unified folder that try to be too smart I guess. I want, for both account, to store sent message locally but other email clients (e.g. my iphone) will still put its sent message in INBOX/OUTBOX. What I'd like to do is when I chose the folders to be used in "Sent" unified folder, to have both INBOX/OUTBOX and the local folder. I do that through the properties of the "Sent" unified folder.

But what seems to happen is that TB seems to only follow what was set in "Place a copy in" from account settings, and even if I have checked the INBOX/OUTBOX for that account, there is no subfolder entry created.

> Sometimes thunderbird crashes/

Please post your crash IDs here from help > troubleshooting information

I'll close this one that was not clearly described