Not a UA but a referer. Anyone know what this is?
https://insertmedia.bing.office.net/
Showed up as the referer for a single image file; log search confirms that I've never set eyes on them before. At least not in the last couple of years. IP, UA, headers seem to be human. Is it part of the MS office family, or something like a search engine? Web page leaves me none the wiser.