There are a couple of ways of acheiving this. Added:- Make sure you have emails in 'Date' order. As your Inbox has so many emails in a single mbox file, I would suggest you move all the ones you wish to keep into another folder first - just as a precaution. Open Inbox. Move all emails you wish to keep into another suitable folder for storage. When Inbox only has the emails you want to delete. select the first email in Inbox Hold down 'Ctrl' key and press 'A' key. This will select and highlight all the emails in the folder. They will appear as x number of 'conversations' in the Message Pane. Click on 'Delete' button. Emails will be marked as deleted. right click on 'Inbox' folder and select 'Compact' This fully removes all the 'marked as deleted' emails. right click on 'Deleted/Trash' folder and select 'Empty Deleted/Trash' If you choose not to move good emails out of Inbox prior to selection, then follow this procedure: Open Inbox Click on oldest email Hold down 'Shift' key and click on the most recent you wish to delete. All emails in between should become highlighted as well. They will appear as x number of 'conversations' in the Message Pane. Click on 'Delete' button. Emails will be marked as deleted. The next part (compacting) is necessary to recover space, but if there is any corruption in the Inbox file, you risk losing potentially all your emails. Suggest you move those good emails out of the Inbox first. It is not usually necessary to move emails in order to compact, but as your Inbox has not been used solely as an Inbox but also for long term storage, then the risk is higher. right click on 'Inbox' folder and select 'Compact' This fully removes all the 'marked as deleted' emails. right click on 'Deleted/Trash' folder and select 'Empty Deleted/Trash'