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"Could not get folder db" is the message. I've tried all the suggestions that google provided - nada

Windows 11 25H2 (OS Build 26220.7271) Thunderbird 145.0 (64-bit)

5 accounts are defined. Some filters work on startup, but new ones do not. Manually running filter results in "could not get folder db"

Hi,

we use Thunderbird for several business e‑mail accounts (for example info@… and similar), all configured as IMAP, and the same mailboxes are used by multiple people on several computers. Our mail server hostname is nickel.studio4web (Studio4web hosting).

We have noticed the following strange behaviour of messages (usually customer orders):

A new message arrives normally in the “Inbox” folder.

After some time, for example the next day, the same message also appears in the “Trash” folder, but it is still visible in “Inbox” at the same time.

We checked the headers; the Message‑ID field is exactly the same in both Inbox and Trash, so it looks like one and the same mail that exists in two folders at once.

In Thunderbird Server Settings we configured the delete behaviour so that messages are either moved to Trash or removed immediately (we tested both options), and after that we ran Compact on both the Inbox and Trash folders. However, some messages still remain simultaneously in Inbox and Trash.

We know that other team members open the same accounts in other clients / on mobile phones or in webmail, but we are not sure whether that alone can explain this double appearance of the same message (Inbox + Trash).

For example, two order emails from 03.12. were in Inbox only on that day, and today we see them also in Trash, while they are still in Inbox. No one remembers explicitly deleting them.

Questions:

Is this behaviour normal for IMAP in Thunderbird, or does it indicate some bug or wrong configuration?

Is there a way to prevent a single message from being present in both “Inbox” and “Trash” at the same time (so that it is either only in Inbox or only in Trash)?

What else should we check in Thunderbird settings or on the mail server (filters, special IMAP options, automatic cleanup, server‑side rules, etc.) to avoid such “duplicate” messages?

Environment:

Thunderbird version: 140.5.0esr

Operating system: Windows 11 Pro

Mail server / provider: nickel.studio4web (Studio4web hosting)

Thanks in advance for any help and advice.

Good afternoon, I am using Thunderbird for many years now. In the last ~2 years I have seen several times the subfolders of the mail folder disappearing from the list on the left panel. All of them are correctly subscribed. I would like to know if there exists a way to recover them different from deleting the account and recreating it. I am currently running Windows 11 Pro 25 H2 with Thunderbird 145.0.

Did anyone experienced such an issue? Thanks Riccardo

I just created a new email account in Thunderbird. I've used T-bird for 15 years. Normally, when I highlight an inbox email and then press the keyboard "Delete" key, the message is sent to Trash. But on this new account, when I press Delete key, the message briefly disappears, but then comes back into my Inbox. It doesn't go to Trash.

I checked the Server setup and confirmed it is setup to move Deleted email to "Trash on xxx@xxxx.com"