Thunderbird not showing new/unread junk emails

Question

Thunderbird fails to sync junk folder unless user clicks on junk folder specifically. How can user sync junk folder automatically, since otherwise there is a chance false positives might go unnoticed?

Thunderbird is latest version 52.2.1 (32 bit) on Windows 10, all folders are subscribed, tried pressing "Get All New Messages" several times, restarted Thunderbird, tried disabling/enabling adaptive junk filter option. Server used is Dovecot IMAP with SUBSCRIBE turned on for the Junk folder. Issue does not happen in other clients whereupon receiving junk message the junk folder shows unread message flag.

Answer 1

It appears Thunderbird does not automatically sync junk or trash folders by default (tested latest stable and beta versions on Windows 10). The solution was to include junk folder in message synchronization settings (offline use settings).

Tools > Account settings > Synchronization and storage > Advanced > Select junk folder.

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Updated for Thunderbird version 102

Right click Junk folder > Properties > Check the option When getting new messages for this account, always check this folder > Press OK

Answer 2

In my case what worked was right click in the account, then "subscribe", and here you select whatever folder you want.

Answer 3

This method worked for me:

1. Right click on "Junk" folder
2. Click "Properties"
3. Check mark "When getting new messages for this account, always check this folder"
4. Click "OK"

This may be different in your Thunderbird version.

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Edit: I found there is an answer which already has this method, but I was unable to see this method in that answer when I was finding the solution, so I am keeping my answer so that others (like me) can see easily.