When sendmail receives a message via SMTP, it
can also receive an envelope identifier as part of the envelope
sender declaration:
MAIL From:<address> ENVID=envelopeID
Here, the MAIL FROM: command specifies the envelope
sender's address. Following that address is the
keyword ENVID= followed by the envelope identifier. Whenever this
identifier is presented and accepted, sendmail
will place a copy of the identifier into this
${dsn_envid} macro.
A badly formed identifier (one that is not properly xtext-encoded,
Section 21.6.2) will be rejected with:
501 5.5.4 Syntax error in ENVID parameter value
For a more complete explanation of the ENVID= keyword, see the
${envid} macro in ${envid}.
Note that this ${dsn_envid} macro is set when mail
is received via SMTP and when the -V command-line
switch (-V) is used to set the envelope
identifier. By contrast, the ${envid} macro is set
only during delivery.
Note that the envelope ID described here is different from the
message ID (as used with the Message-Id: header,
Message-ID:), and different from the queue ID (which
identifies a queued file, Section 11.2.1).
One possible use for this ${dsn_envid} macro might
be to syslog the envelope identifier. Another
possible use might be to include a header showing the envelope
identifier. Consider these mc configuration
lines that do the latter:
LOCAL_CONFIG
H?${dsn_envid}?X-DSN-ENVID: ${dsn_envid}
C{persistentMacros} {dsn_envid}
Under V8.12 and above sendmail, the
X-DSN-ENVID: header in the preceding example will
be included only if the message was received with an envelope
identifier that caused the ${dsn_envid} macro to
have a value. The C line in the preceding example
adds the name {dsn_envid} to the
$={persistentMacros} class. Without this line, the
value in the ${dsn_envid} macro would not survive
queueing.
${dsn_envid} is transient. If it is defined in the
configuration file or in the command line, that definition can be
ignored by sendmail. Note that a
$& prefix is necessary when you reference this
macro in rules (that is, use $&{dsn_envid},
not ${dsn_envid}), but a $&
prefix is not necessary in header definitions.
