Use MTA_ENV_TO

Intermediate processing channels should use the MTA_ENV_TO item code with mtaEnqueueTo() rather than the MTA_TO, MTA_CC, and MTA_BCC item codes. This tells the MTA that the recipient address being specified should be added to only the message’s envelope and not also to a Resent-To:, Resent-Cc:, or Resent-Bcc: header line. Example 4–3, and Example 5–2 illustrate the use of the MTA_ENV_TO item code. Both of those examples represent intermediate processing channels which are handling a previously constructed message. As such, they do not need to alter the existing message header.