The MAIL ESMTP command can optionally be followed by an RFC1891 ENVID envelope identifier: MAIL From: < address > ENVID= envelopeID ENVID is used to propagate a consistent envelope identifier (distinct from the Message-ID : header, Message-ID:) that is permanently associated with a message. The Z line holds that ENVID envelope identifier information: Z envelopeID The ENVID information needs to be held separately from the S sender line because sendmail has no way to determine in advance whether a recipient host speaks ESMTP. There must be only a single Z line in any qf file. The ${envid} sendmail macro (${envid}) also stores the ENVID value. |