Inbox is for new incoming mail and should not be used as a general store. Suggest you create new folders and organise/move your emails. Please understand that what appears as an Inbox folder in the Folder Pane, in reality, it is just a simple single mbox text file with emails written one after the other in the order downloaded. It is exceptionally risky to have a single file (not folder) of such large size. Also please note: when you delete an email, it is marked as deleted and hidden from view. You may see it in the 'Trash', but a copy is still in the 'Inbox' this facilitates recovery if deleted in error. So all of those 'marked as deleted' emails could still be taking up space and bloating your Inbox. To completely remove all of those 'marked as deleted' but hidden emails, you need to compact the folder on a regular basis. If you have not done this in a while and you really have loads of emails in the Inbox either because you have not managed them or hidden deleted emails occupy space, I would recommend you move all emails out of Inbox into suitable folders. Delete what you do want. Please note: Usually, you do not need to move everything prior to compacting, but on such a large file, if anything is slightly corrupted, you could lose a lot of emails. Empty 'Junk'. Then do compacting: * right click on 'Inbox' and select 'Compact' * right click on 'Junk' and select 'Compact' This should give you a fresh, clean Inbox.