I get a lot of those myself and have gotten them pretty much the whole time I have owned websites and blogs that had contact forms.I keep getting a lot of emails through the contact form on my blog for SEO services. They are saying things about how there is room for improvement or that they can get me onto the first page of Google.
It seems like a scam type of thing but I really don't know if they are or not.
There is really no way to know for certain if they are legitimate or not without trying to look them up. Personally I would rather stick to places that are not sending spam emails to try to get work.