As a part of the STARTTLS form of authentication and encryption,
certificates are usually exchanged. The certificate presented by the
other side is signed by a certificate authority, and this
${cert_issuer} macro is assigned the distinguished
name (the DN) of that certificate authority. That value might look
like this:
/C=US/ST=California/L=Berkeley/O=Sendmail.org/CN=Sendmail+20CA/
See Section 10.10.8.1 for an illustration of one use for
${cert_issuer}. See Section 21.6.2
to find how and why the value in this macro undergoes special
translation.
${cert_issuer} is transient. If 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 $&{cert_issuer},
not ${cert_issuer}).
