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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
+}
+