======Spam Filter Rules: AddHeader======
^Statement  |AddHeader |
^Version  |2.1.7+ |
^Purpose  |Allows you to add, replace or remove the specified header line in the message headers |

The **AddHeader** statement requires the full header line in one continuous string, in the format
  AddHeader "<full header line>"

  * If the header line is present:
    * It will be replaced if an alternative value is specified.
    * It will be removed if no value is specified.
  * If the specified header is not already present, it will be inserted at the end of the headers.
  * **AddHeader** should not be used where the header name may appear more than once (e.g. "Received: ...").

From VPOP3 v6.20 onwards, the header modifier format has been extended:
  * If you prefix it with -, it will be added at the the start of the final headers
  * If you prefix it with +, it will be added at the end of the final headers
  * If you prefix it (after the -/+ above) with "{"<username>"}" (eg ''{bob}Subject: Bob's new subject'' ) it will only be added to the headers when placed into that user's mailbox
  * If you prefix it with #, it will remove the header if the data matches the regular expression specified in the modifier's data - eg ''#Bibble: ^[a-z]{5}$'' - otherwise the original header will be left in place
  * 

=====Examples=====
Changing the subject header
<code>
AddHeader "subject: VPOP3SPAM ${Subject}"
</code>

Removing a header line, by not setting a value
<code>
AddHeader "X-MyHeader:"
</code>

Changing the value of a header, or inserting it if it does not already exist
<code>
AddHeader "X-MyHeader: The new value of the header named X-MyHeader"
</code>