Just because it passes MS servers doesn't mean it is genuine. Only way to check is to call Microsoft's validation team & check. They will tell you if it is genuine.
There are millions of frauds. If it was £3.99 I would suggest it is a fake/fraud.
There is a massive market in used licensing which is totally genuine but they are not £3.99. They are much cheaper often half price for mainly one generation behind current versions. We bought a chunk of Outlook 2013 volume licences for a customer last year that were half the cost of Outlook 2016. They came from the liquidation of Phones2u/Phones4u so all very genuine. Their are software companies that buy the licenses from the liquidator & they are resold. We had to fill out forms to change the ownership from Phones2/4u to our customer.
If you only value your office use at £3.99 then don't expect much. You have to be very very careful as well these days. We know many scenarios where this happens & they send you a download link to download the ISO or their EXE file. You install it & install all their Trojans, key loggers, malware, viruses & everything. You may not know it but in 3 or 6 months or more you will!
In my opinion it is just not worth it as the risks far outweigh the benefits. Off the top of my head a perpetual copy of Home & Student is 75 quid. Open office is free & very usable. Online versions of Office are free. You could buy one copy & install it on one machine and 'remove' it from that to allow you to install on a second. MS's activation/validation servers will generally activate a product over their internet system 3 times before this stops then you need to call them to do over the phone. We often have to call them to say it has been removed from an old machine we have replaced with a new one then installed in the new one. They give you a new code to validate activation in the new one fine which is quite a common occurrence.
Be careful out there guys as our security and care/attention to it is very poor in this country at the moment. Banks are just as bad & often very insecure. It is part of the reason I set up the new Access Control & security business last year. The next 5 years will certainly be very interesting!
