It may be hard to know whether your email marketing business is breaking spamming laws through your policies, but the importance of you not doing so cannot be underestimated. Going into the specifics may take you a while, but there are a few questions that you can ask yourself.
See details here Be clear with your target

Upon what you believe will be your first contact, do not try to be deceptive. Explain to them through the text exactly what your business - your objective, your purpose - is about without it feeling like you're telling your life story. Some companies may believe just slightly bending the truth will mean they stay on the right side of the law but in reality, the slightest sign of this will land them in trouble.

Include an address

There has to be a registered address on all emails, otherwise customer feedback relies on an internet connection; which cannot always be guaranteed. Make sure there is an address for your company, perhaps at the bottom of the email, to give your customers another way to contact you.

Offer an exit option

At any point, your customers should be able to be opt out of receiving emails. A common tactic is to bury this into the deepest realms of the website; but chances are, if your customer wants to opt out of receiving your messages, they'll be able to do it somehow. The biggest of businesses always include a tab or a button at the end of emails to give their customers easy access of cancelling their subscription to updates; and it's moves like that which make them the biggest, most reputable companies.