Lets say I have a database of 60,000 emails.
I would like to send them an email notifying them of a new related service (similar to what they've signed up) which adds value to what they already signed up to.
I know most of them would welcome it but they did not opt-in for this new related service. I don't want to send out the email invite only to find out I got into some Spam Act trouble.
What is a friendly way to reach these targetted audience?