The message envelope contains the envelope From: address, and the list of envelope To: addresses. The envelope is created by the SDK as the message is enqueued. The addresses to be placed in the envelope must conform to RFC 2822. The envelope To: addresses are often referred to as envelope recipient addresses.
Programs should rely solely upon the MTA SDK routines to read and write envelope information, since the queued message file formats are subject to change. Using the SDK routines insulates programmers from format changes.
The routines mtaEnqueueStart( and mtaEnqueueTo( are used to construct a message envelope.