sort mail by date. Select the first one with your mouse. Hold the shift key scroll to the place you want to select the last one. Select it and everything in between is selected. Release the shift Key Note here: I personally think archiving EML files in folders on the hard drive a waste. They are difficult to sort through and locating the correct one is basically left up to that dog of a search tool Windows search. Once you locate one, there is no simple process to locate the rest of the thread. Thunderbird has an archiving tool and it is actually quite a robust archiving solution. In the case of POP mail accounts, mail is already on your hard disk, and archiving them does nothing to free up server space. It just moves them around for easier management In the case of IMAP mail accounts, setting the archive folder in account settings to the archive folder in Local Folders (A manual change as the default is always archive within the account) moves mail from the account folders, deletes mail from the server and generally frees up space server side. I suggest you read this http://mzl.la/1g2pBB5