Z line
DSN ENVID envelope identifier V8.7 and later
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: on page 1159)
that is permanently associated with a
message.
The Z line holds
that ENVID envelope identifier information:
ZenvelopeIDThe 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} on
page 823) also stores the ENVID value.
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