I have a list of personal/professional contacts in gmail that have not opted-in to anything. These are people I have known for years. How do I move those who might be interested from a contact list in gmail to a subscriber list in ConvertKit without (a) annoying them or (b) running afoul of ConvertKit's rules (... or CAN-SPAM, for that matter)? Do I need to use a tool like GMass to send a single email blast with a link to my landing page for my newsletter? Is that legit?