If you have a POP mail account then Thunderbird can only access and download emails from the server Inbox. This is how all pop accounts work no matter what email client is used. Pop accounts do not have access to any other folder on the server. Pop accounts do not synchronises any folder with server which means the server Inbox can look entirely different from the pop account Inbox. It is normal to download from server Inbox and the emails on server are deleted, but there are settings which you can use to 'keep messages on the server' and many people use those settings.

This means if the server decides something is junk/spam and moves it out of the Inbox to another folder on server, there is no way a POP account can know it exists.

All pop accounts will have a 'Junk' folder and any email received in the 'Inbox' that is determined as junk either by Thunderbird's Junk settings or by a Message Filter you created or by a manual mark as Junk will move it to the pop account Junk folder as per Account Settings > Junk Settings.

It's impossible to switch off the server spam filter, so if server decides it's spam then it gets moved.

There are really only two options. 1. Log onto webmail and mark email as not junk/spam to get it into the Inbox, then in Thunderbird click on 'Get Messages' to download. Or just log on to webmail and read junk emails in situ. 2. Consider using an IMAP account.

You cannot simply swap the server settings to change a pop into an imap.

You would need to get copies of all emails that are currently in the pop account copied into suitable folders in the 'Local Folders' mail account - you could always delete them later if you find you have duplicates.

Then remove the pop account via Account Settings - select pop account, click on 'Account Actions' and select 'Remove account'.

Create a new Existing Mail account and set it up as an IMAP mail account. https://support.mozilla.org/en-US/kb/automatic-account-configuration

Info on imap synchronisation: https://support.mozilla.org/en-US/kb/imap-synchronization

IMAP is very different, emails are stored on server and imap account folders synchronise with server folders to display what is on server. You can choose to download headers or full copies of emails. You can also do this on a per folder basis. If you download full copies, it means you can still read emails in Offline mode and it also means you can create a backup of the profile, which includes mail account, emails (assuming you have full copies as they will be stored in mbox files), contacts, message filters, preferences etc etc. Note, if you delete an email in an imap account it will get deleted off server when folder next synchronises and also vis versa, you delete an email off server via webmail or phone or another imap account and it will also get deleted from Thunderbird. Do not rely on an imap account downloading full copies as a true separate copy because those folders are not independent of the server.

I advise anyone using an imap or pop account to periodically create a backup.

Thanks for your comprehensive reply. I thought I had an IMAP account, but maybe not. The server setting (for picking up mail) is "imap-mail.outlook.com", port 993. But if I understand correctly what you have written, then maybe this was originally created as a POP account, and then the server settings changed. If so, that would certainly account for the behaviour seen. I'll have a look at recreating the TB account as you suggest.

You can tell if it was set up as imap originally.

In Account Settings > Server Settings for the account This would tell you how it was originally created. Server Type: Does it say 'IMAP' or 'Pop' mail server ?

At the bottom you will find 'Local directory:' Does it say you are using the 'ImapMail' folder or the 'Mail' folder ? example: C:\Users\User Account anme\AppData\Roaming\Thunderbird\Profiles\123abc4.default\ImapMail or C:\Users\User Account anme\AppData\Roaming\Thunderbird\Profiles\123abc4.default\Mail If 'Mail' then originally set up as POP.

Usually, servers have a folder called 'Spam' or 'Spam Mail' or 'Bulk Mail' but on occasions do have a 'Junk' folder. Do you see folders with name 'Junk' or 'Spam' when you log on to the webmail account ? Is there only one of these folders?

Info on outlook.com webmail block or unblock: https://support.microsoft.com/en-us/office/block-senders-or-mark-email-as-junk-in-outlook-com-a3ece97b-82f8-4a5e-9ac3-e92fa6427ae4

Check to see if the imap account Junk in Thunderbird needs index rebuilding.

• Right click on 'Junk' folder and select 'Properties'
• Click on 'Repair Folder'
• click on 'OK'

select another folder and then reselect 'Junk' If email shown in webmail account appear then all is ok.

Check the 'Junk' folder is properly subscribed.

• Right click on imap account name and select 'Subscribe'
• Click on 'Refresh'
• Select 'Junk/Spam' (whatever it is called) and click on 'Subscribe'
• click on 'OK'

Check setting in Thunderbird to see you really are using the server 'Junk/Spam' folder.

• Right click on imap account name and select 'Settings'
• Select 'Junk Settings'

bottom under 'Destination and Retention'

• Select 'Other' and choose 'Junk/Spam on account name' (where it is the same name as used on server.)

Restart Thunderbird.

Turns out it was the "subscription" that was wrong. When I selected "Subscribe", sure enough "junk" was in the list with a check mark. But then I noticed that as well as "Junk", there was also "Junk Email". Selected that, and as if by magic, my junk e-mail appeared. In fact everything else was already correct (Imap, Junk settings, etc.). Why there were two Junk items, I don't know, but at least it's working now.

All that's left is to move all the saved mail back to the Inbox, but maybe I won't bother - there's enough in there already!

Many thanks, Toad-Hall. You've helped fix something which I know for a fact has lost me things marked as junk, but not actually junk, in the past.