Situation: An existing customer has not opted in to receive specific emails, but your company has obtained the customer's email address through an email append or additional customer maintenance (e.g., email address provided during a transaction). The customer is familiar with your company and has a business relationship with it.
Stance: This is the safest of all scenarios. Since the email address has been provided, that could be considered an opt-in. However, if you go this route, be prepared for an exodus after the first mailing.
Solution: Send a confirmation email allowing the recipient to opt-in for future email communications or opt out immediately.
Next: When it's OK to send email
