Son helping his father out with a mistake in thunderbird. He had an old email address from his old ISP set up as a POP account; he then got a new gmail account and added that as IMAP. Today he tried to move all the folders from his old account (by selecting several at a time and drag&dropping them to his gmail account). For the most part this work, but some folders are completely gone, and others are missing files past a certain date. In particular, for one folder he has files only up to June 2013. Looking around in the profile folder I can't find any traces of the old mbox file; we had an old archive of this particular folder & have emails up to December 2014, so we're now missing 2015-2016. Any advice on where else we might be able to recover this info from? Thanks in advance.