When the message is about to be written out, the command specified by
&%transport_filter%& is started up in a separate, parallel process, and
the entire message, including the header lines, is passed to it on its standard
-input (this in fact is done from a third process, to avoid deadlock). The
-command must be specified as an absolute path.
+input (this in fact is done from a third process, to avoid deadlock).
+The command must be specified as an absolute path.
+
+The process run by the command must use its standard input as the message
+data to be transformed, and write the results on its standard output.
The lines of the message that are written to the transport filter are
terminated by newline (&"\n"&). The message is passed to the filter before any
Verification of DKIM signatures in SMTP incoming email is done for all
messages for which an ACL control &%dkim_disable_verify%& has not been set.
+
.cindex DKIM "selecting signature algorithms"
-Individual classes of signature algorithm can be ignored by changing
+Individual classes of DKIM signature algorithm can be ignored by changing
the main options &%dkim_verify_hashes%& or &%dkim_verify_keytypes%&.
The &%dkim_verify_minimal%& option can be set to cease verification
processing for a message once the first passing signature is found.
of this section can be ignored.
The results of verification are made available to the
-&%acl_smtp_dkim%& ACL, which can examine and modify them.
+&%acl_smtp_dkim%& ACL, which (for complex needs) can examine and modify them.
A missing ACL definition defaults to accept.
By default, the ACL is called once for each
syntactically(!) correct signature in the incoming message.
&%dkim_verify_signers%& (see above).
.vitem &%$dkim_verify_status%&
+So long as a DKIM ACL is defined
+(it need do no more than accept, which is the default),
+after all the DKIM ACL runs have completed, the value becomes a
+colon-separated list of the values after each run.
+The value is maintained for the MIME, PRDR and DATA ACLs.
+
Within the DKIM ACL,
a string describing the general status of the signature. One of
.ilist
set dkim_verify_reason = hash too weak or key too short
.endd
-So long as a DKIM ACL is defined (it need do no more than accept),
-after all the DKIM ACL runs have completed, the value becomes a
-colon-separated list of the values after each run.
-This is maintained for the mime, prdr and data ACLs.
-
.vitem &%$dkim_verify_reason%&
A string giving a little bit more detail when &%$dkim_verify_status%& is either
"fail" or "invalid". One of
.endlist
-In addition, two ACL conditions are provided, usable only in a DKIM ACL:
+In addition, two ACL conditions are provided:
.vlist
.vitem &%dkim_signers%&
ACL condition that checks a colon-separated list of domains or identities
for a match against the domain or identity that the ACL is currently verifying
-(reflected by &%$dkim_cur_signer%&). This is typically used to restrict an ACL
+(reflected by &%$dkim_cur_signer%&).
+This condition is only usable in a DKIM ACL.
+This is typically used to restrict an ACL
verb to a group of domains or identities. For example:
.code
.vitem &%dkim_status%&
ACL condition that checks a colon-separated list of possible DKIM verification
-results against the actual result of verification. This is typically used
+results against the actual result of verification,
+given by &$dkim_verify_status$& if that is non-empty or "none" if empty.
+.new
+This condition may be used in DKIM, MIME, PRDR and DATA ACLs.
+.wen
+
+A basic verification might be:
+.code
+deny !dkim_status = pass:none:invalid
+.endd
+
+A more complex use could be
to restrict an ACL verb to a list of verification outcomes, for example:
.code
The possible status keywords are: 'none','invalid','fail' and 'pass'. Please
see the documentation of the &%$dkim_verify_status%& expansion variable above
for more information of what they mean.
+
+The condition is true if the status
+.new
+(or any of the list of status values)
+.wen
+is any one of the supplied list.
.endlist
git://git.exim.org / exim.git / blobdiff