It would be super helpful if you're able to be compatible with Zapier. We use Redtail as CRM, which is integrated with Zapier. Would be fantastic that when a new contact is created in Redtail that the same contact is created in Mailbutler, or visa versa.
Basic API access that integrates with Zapier would be quite useful to fill some feature gaps like external contact synchronization or updates. E.g., on contact create or update create a new contact in google contacts, or add to google sheet, etc.