CAN-SPAM Act of 2003 ... Keeping clean for business mails
I get quite of bit of email from folks who have "harvested" my name in a personal way (not mass harvesting). They know at least who I am enough to target their message. We're talking "company" messages here (not spammers). The companies range from telephone companies, technology companies, office suppliers ... the usual bunch. Many are from an individual within the company who is "cold calling" via email rather than phone. The mails are not exciting enough to reprint here, but anyone in a company probably gets these.
The major problem with these messages is that most don't fully conform to the CAN-SPAM Act of 2003 (Good round up at Wikipedia - http://en.wikipedia.org/wiki/Can_Span).
For example, they usually don't provide an opt-out. Now, even without an explicit opt-out button, putting full contact information (including postal address), can cover the bases, but many forget to do this. The best approach: put a soft opt-out message (i.e., "just reply back and say remove if you don't want to hear from me again") to at least acknowledge the reader... and stay legal!