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Editheader Extension

Relevant specifications
=======================

  RFC5293 - doc/rfc/editheader.rfc5293.txt

Description
===========

The editheader extension [RFC5293] enables Sieve scripts to delete and add
message header fields, thereby allowing interaction with other components that
consume or produce header fields.

Configuration
=============

The editheader extension is not available by default and needs to be enabled
explicitly by adding it to the sieve_extensions setting.

The following settings can be configured for the editheader extension (default
values are indicated):

sieve_editheader_max_header_size = 2048
  The maximum size in bytes of a header field value passed to the addheader
  command. The minimum value for this setting is 1024 bytes. The value is in
  bytes, unless followed by a k(ilo).

sieve_editheader_forbid_add =
  A space-separated list of headers that cannot be added to the message header.
  Addition of the `Subject:' header cannot be prohibited, as required by the RFC
  specification. Therefore, adding this header to this setting has no effect.

sieve_editheader_forbid_delete =
  A space-separated list of headers that cannot be deleted from the message
  header. Deleting the `Received:' and `Auto-Submitted:' fields is always 
  forbidden, while removing the `Subject:' header cannot be prohibited,
  as required by the RFC specification. Therefore, adding one of these headers
  to this setting has no effect.

sieve_editheader_protected =
  A space-separated list of headers that cannot be added to or deleted from
  the message header. This setting is provided for backwards compatibility. It
  is a combination of the sieve_editheader_forbid_add and
  sieve_editheader_forbid_delete settings. The same limitations apply. 

Invalid values for the settings above will make the Sieve interpreter log
a warning and revert to the default values.

Example
=======

plugin {
  # Use editheader
  sieve_extensions = +editheader

  # Header fiels must not exceed one 1k
  sieve_editheader_max_header_size = 1k

  # Protected special headers
  sieve_editheader_forbid_add = X-Verified
  sieve_editheader_forbid_delete = X-Verified X-Seen
}