Hi @BS69,
Will try my best to help out here :)
First, I’m making an assumption that these contacts are US-based. Otherwise, if marketing consent was not explicitly expressed, depending on the region (e.g. Europe and GDPR), it could be non-compliant to be reaching out asking for marketing consent.
Depending on the size of the database, and if the customer email database spans several years and/or contains many contacts who have not been consistently receiving emails consistently, it could be a safer approach to email this group in batches vs. all in one send. This could reduce the risk of negatively impacting your sender reputation.
It would also allow you to monitor engagement of the initial batches to see if it’s worth continuing to send to this audience.
Your approach of an “opt-in” campaign vs. an “opt-out” one is spot on and what I’d recommend to ensure only active and engaged contacts that want to receive marketing emails remain on the list. Including an opt-in link for the recipient to click in the email would be best practice and one I’ve seen typically executed in these cases.
Let me know if I can be of further help here!
Cheers,
Bobby