When you delete an email, it is marked as deleted and hidden, but remains in file. To clear all hidden marked as deleted emails you need to compact the folder to remove them and reduce file size. Emails are not stored in individual files. In your case you have one single text file document (not a folder) that contains all your emails. When emails are downloaded, they are written to the file one after the other in the order downloaded. This is somewhat risky to have everything in one text file. As you have all emails in the Inbox, which is really designed to contain new incoming mail and not be a general storage, I would advise you do the following as it is unknown how often you have been compacting nor whether the Inbox has any unknown corruption of the file. Keeping all emails in the Inbox is risky; especially if you use an AV product which is allowed to scan thunderbird folders and files or scan incoming mail. * Move all good wanted emails into suitably named folders. * Then use 'Ctrl' + 'A' to select all remaining unwanted emails. * they will appear as 'conversations' in the Message Pane. * click on 'Delete' button * then right click on Inbox and select 'Compact' to completely clear the Inbox. '''If you wish to keep all good emails in Inbox anyway regardless of risk:''' (It might be a good time to create a back of your Profile first) To select various emails: * Holding down the 'Ctrl' key * Left click to select/highlight various emails in list. To select a block of emails: * Select first one you want to delete. * Hold down 'Shift' key * click on the last one and all emails in between become highlighted. they will appear as 'x number of conversations' in the Message Pane. click on 'Delete' button Remember: right click on Inbox and select 'Compact' to remove deleted items completely from the Inbox. Some useful info: * http://kb.mozillazine.org/Keep_it_working_%28Thunderbird%29 * http://kb.mozillazine.org/Compacting_folders