In the early 2000s the US Federal Trade Commission (FTC) began regulating SPAM. Eventually, the CAN-SPAM Act required the Commission to issue regulations “defining the relevant criteria to facilitate the determination of the primary purpose of an electronic mail message.” The CAN-SPAM Act applies almost exclusively to “commercial electronic mail messages”.
Due to these regulations emails are closely monitored and legally filtered to protect consumers from unwanted emails. These rules can make it very easy for your email communications to be flagged as SPAM. The good news is, the FTC also publishes guidelines to help you send safe and effective emails that avoid breaking SPAM laws:
We highly recommend our customers review and follow the guidelines described in the link above.