I received an email similar to the one described here, thanking me for a recent premium payment to Humana. Of course, I don't have insurance with Humana.
Is this likely to be a scam? If so, how does this scam work? What will they gain from this?
I thought it might be phishing. The links in the email all go through links.mkt3525.com (the same redirector mentioned in the linked web page), but they seem to redirect to the real www.humana.com site. Redirections like this in emails are not that suspicious -- our company uses a couple of mass email services (SendGrid, Mailify) and they rewrite links in emails so they can provide reports on how many recipients click on your links (this is mostly useful for marketing emails).
The most suspicious thing was that the email was sent to my gmail address, which I rarely give out (I generally only use it when I create accounts at sites that want to link to a Google account). It also doesn't have any information identifying my account -- it doesn't address me by name, or show the last N digits of an account number.