I have not seen the email first hand, but can imagine that it is a phishing scheme trying to get you to click a link.
It may not actually be from the rental car company at all, just a very convincing lookalike.
Standard email rules apply...
I used TopSantiago also and found them to be very easy (and flexible) to work with. Great communication, too. I've been told they're more expensive but I was so happy with them that I didn't search any further.
This site is run by Ivar at in Santiago de Compostela.
This site participates in the Amazon Affiliate program, designed to provide a means for Ivar to earn fees by linking to Amazon