Who is the mail provider, and is the account POP or IMAP?

Hello, my provider is iinet in Australia and the account is IMAP, any help appreciated

Right-click the account in the Folder Pane, Subscribe, Refresh, check the box for the Sent folder. To add folders that don't appear in the Subscribe window, New Folder... from the account right-click menu.

Thanks, but when I right click Subscribe and refresh, no folders appear. Only a "please wait". I waited but nothing. Other email accounts show folders as you say. The only mail folder with no lock showing on the envelope of the email is Local Folders. I can add folders here as you suggest, but not to the other email accounts. Am thinking to delete Thunderbird program and start again, but fear I will lose everything. The Thunderbird is fully up to date with latest update. Appreciate your help.

What are your settings? They should be: incoming IMAP mail.iinet.net.au on 143, STARTTLS, normal password, User Name = email address; outgoing mail.iinet.net.au on 587, STARTTLS, normal password, User Name = email address. The lock on the account icon indicates the connection is secure (STARTTLS).

https://help.iinet.net.au/email-setup-thunderbird

Disable a VPN if you have one, and add the TB profile folder as an exclusion or exception in antivirus settings. They might be blocking access to the mail server and showing the folder list.

The lock you describe means the account connection is encrypted. As you local folders are on your local machine they are obviously not encrypted.

Have you tried with out your anti virus program?

Thanks Matt and sfhowes, you have both opened my eyes to look at my firewall protection that Norton runs for me. I am having trouble getting to the Norton settings to see if I can tweek the Automatic Program Control as I suspect this is where the problem is. I am able to see these emails and all folders on iphones, ipad, but not this Win 10 laptop protected by Norton. I will try and work my way through the Norton configuration. Thanks to you both

For Norton settings, see https://support.mozilla.org/en-US/questions/1336858