No it is a scam. Airbnb don't send emails. They don't ask for payment off site.
All their communications relating to bookings goes through their online messaging system on their platform.
If you want to book through Airbnb, the only way to do this is through their website. If you want to use Airbnb choose a Superhost who has been hosting for a year or more and has lots of five star reviews.
Airbnb is really set up for short term rather than long term bookings.
If you want to rent long term I would recommend you could through a reputable estate agent in Barcelona.