The padlock indicates that that account uses a secure connection and has nothing to do with being locked.

If there is a padlock on the mail account name, it means that the mail account uses a secure connection. eg: SSL In this case, the padlock does not mean that it is locked.

However, you mention a padlock on an accounts Inbox folder and unable to move emails into the folder.

Maybe the file is marked as 'read only'.

Try this: Make hidden files and folders visible

• http://kb.mozillazine.org/Show_hidden_files_and_folders

In Thunderbird

• Help > Troubleshooting Information
• click on 'show folder' button

a new window opens showing your Profile folder

• Close Thunderbird now - this is important

• click on Mail folder
• click on Account name
• look for 'Inbox' file - not 'Inbox.msf'
• right click on Inbox file and select 'Properties'
• Is the 'read only' checkbox selected ?
• If yes, uncheck the box
• Click on 'Apply'
• Click on 'OK'

close the profile window - top right X

open Thunderbird Is the Inbox folder accessible?