Hello website owner, your website is terrible. You're not #1 on Google for all keywords. Pay us money and we'll guarantee #1 placement.To someone like me or any other ethical SEO expert these emails are laughable. Jade Sholty wrote a good summary here which I recommend reading. These "companies" (many aren't even legitimate companies) send these emails out to every website contact they can find. This is one of the reasons we recommend registering client domain names with our own contact info, so there is a lower chance that our clients will get sucked into one of these scams. The truth though, is that the wording seems quite scary to the untrained reader. Someone who knows very little about SEO or website structure is only going to see "my website needs to be improved right now". There are a handful of reputable SEO companies out there, but like anything else, a good rule of thumb is that if you're going to buy a product/service from someone, either you call/email them to buy it, or you do some due diligence before pulling the trigger on someone who is soliciting you.
Like Jade mentioned in her own article, I too have occasionally called these companies to see how they present themselves over the phone. I have yet to speak with anyone who knows much about legitimate SEO, yet they continue to (successfully) acquire clients on occasion. PT Barnum had it right, but I'm still trying to do my part and convert some of those suckers into educated dealers who are able to hang on to their money in the face of spammer snake oil salesmen.
Another recommended article is here, and talks about questions to ask your SEO provider. Most of the "bad companies" can't even answer half of the questions. Can your provider?