Just because your boss asked you to do something that many people HATE, doesn't make it better.

People handing over their email address in exchange for user registration or to gain access to a trial version of your product are not interested in receiving sporadic advertising for the next N years.

People are inundated by unwanted email every day, from companies that claim, like Dracula, "but you said I could come inside." Some people don't mind, but some of your target customers will already have very negative reactions to ANY marketing email, so it is incredibly important that you go out of your way to make it clear that you are trying to communicate something that will benefit the recipient, not just a sales pitch you can justify legally sending them.