We are making changes to the way we handle headers when sending with SMTP, ensuring that the recipients visible in your messages' To and Cc headers match those shown to final recipients. This change only affects SMTP sending, does not impact API sending, and will not affect recipients who send single emails or use Postmark as a mail relay from an internal server. For most senders, this change will not have an impact, but we encourage you to review your sending integration ahead of the release.