OpenSend docs
Audience Properties
Properties define custom fields stored on contacts. They are useful for personalization, filtering, support context, and automation conditions.
Examples
plan: free, pro, enterprisecompany: customer organizationsignup_source: landing page or referrallast_seen_at: application timestamp
Best practices
Keep property names stable and documented. Avoid high-risk sensitive data such as passwords, tokens, medical data, or payment details. If a value is only needed for one email, pass it as a template variable instead of storing it permanently on the contact.