Ineffective SEO E-Mail Campaigns at ClickZ from Shari Thurow is a nice, fresh reminder of all those pitches you get for SEO services via email that you can safely delete. No, you almost certainly don't need to worry that they are kindly informing you that you aren't ranking for a particular term!
Shari doesn't get into it, but warnings that you aren't "found" on a search engine our that your listing may be in "trouble" or "vulnerable" can almost certainly be ignored, as well. In fact, rather than list and dissect everything, just remember this. I'd say 99.9 percent of the unsolicited email you get pitching you on search marketing services or alerting you to some type of SEO problem can get deleted.
Good SEM firms are in high demand and aren't going to be cold-calling you by phone or via email. The ones that do, I'd be wary of them and certainly wouldn't lose sleep worrying if something they claim is a problem with your site really is.