what mail provider?

AussieDenis said

I cant use IMAP on my account, so need to 'leave messages on server - until I delete'. But I cant download all messages only new ones.

Go Daddy

re :I cant use IMAP on my account

So you have a POP mail account ? Pop mail accounts can only access and download from the server Inbox to the mail account Inbox. This is not a TB quirk, it is how all POP mail accoutns work.

There is a workaround, which you would only need to do once.

In thunderbird: Prepare Inbox - this makes life easier. Move all emails out of Inbox into other suitable folders. Delete what you do not want. When Inbox is empty: right click on Inbox and select 'Compact'

Logon to webmail account. Select a folder with emails and move them into the Inbox.

In Thunderbird click on 'Get Messages' to download those emails to your Inbox. create a folder and move all of those emails into that folder, so Inbox is empty.

Repeat this action of moving emails from a server folder into the server Inbox and downloading to pop mail accoutn Inbox.