Can Sieve Scripts Use Functions Defined Via Mapping Tables?

Yes, Sieve scripts can use functions defined via mapping tables. In particular a Sieve script can use a function that is implemented as a mapping table that does a dns_verify routine call to query spamhaus.

Although this mapping-table-as-Sieve-function functionality has existed for quite awhile, the syntax doesn't settle down until Messaging Server 6.3. For Messaging Server 6.2, you can do this with a bit of an incompatibility in the variables usage. (This document does not address releases prior to Messaging Server 6.2.)

• In Messaging Server 6.3, to have a Sieve function that is a mapping table, create a mapping table named FILTER_function-name, for example:

  FILTER_foo
  
    a     b$Y
  

  A Messaging Server 6.3 Sieve script can then accomplish something like the following:

  require "variables";
  if foo "a" {set "foo-result" "{$0}";
              set "foo-flags" "{$1}";
              if string :is ${foo-result} "b" { hold; }
             }
  

  This Sieve script sets foo-result to b and foo-flags to Y, and .HELD the incoming message.

• In Messaging Server 6.2, to have a Sieve function that is a mapping table:

  require "variables";
  if foo "a" {set "foo-result" "{$1}";
              set "foo-flags" "{$2}";
              if string :is ${foo-result} "b" { hold; }
             }
  

  Note the different variable numbering.

In general, the idea is to have a mapping table (say FILTER_spamhaus) that uses a dns_verify callout to query spamhaus. Have your Sieve script check for relevant header lines that might have a source IP, then call the spamhaus function (which is the FILTER_spamhaus mapping) passing in to the function/mapping the source IP your script found (and stored in one variable) and getting back a spamhaus result in another variable; check that returned variable and based upon it do something useful, whatever you consider useful: discard the message, reject it, .HELD it with the "hold" action, do a "spamadjust", and so on.