Vacation Extension

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

	RFC5230 - doc/rfc/vacation.rfc5230.txt
	RFC6131 - doc/rfc/vacation-seconds.rfc6131.txt

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

The Sieve vacation extension [RFC5230] defines a mechanism to generate
automatic replies to incoming email messages. It takes various
precautions to make sure replies are only sent when appropriate. Script
authors specify how often replies are sent to a particular contact. 
In the original vacation extension, this interval is specified in days
with a minimum of one day. When more granularity is necessary and 
particularly when replies must be sent more frequently than one day, 
the vacation-seconds extension [RFC6131] can be used. This allows 
specifying the minimum reply interval in seconds with a minimum of zero
(reply is then always sent), depending on administrator configuration.

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

The vacation extension is available by default. In contrast, the
vacation-seconds extension - which implies the vacation extension when 
used - is not available by default and needs to be enabled explicitly by
adding it to the sieve_extensions setting. The configuration also needs
to be adjusted accordingly to allow a non-reply period of less than a 
day.  

The vacation and vacation-seconds extensions have their own specific
settings. The settings that specify a period are specified in
s(econds), unless followed by a d(ay), h(our) or m(inute) specifier
character. 

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

sieve_vacation_min_period = 1d
  This specifies the minimum period that can be specified for the :days
  and :seconds tags of the vacation command. A minimum of 0 indicates that
  users are allowed to make the Sieve interpreter send a vacation response
  message for every incoming message that meets the other reply criteria
  (refer to RFC5230). A value of zero is however not recommended. 

sieve_vacation_max_period = 0
  This specifies the maximum period that can be specified for the :days tag
  of the vacation command. The configured value must be larger than the
  sieve_vacation_min_period setting. A value of 0 has a special meaning: it
  indicates that there is no upper limit. 

sieve_vacation_default_period = 7d
  This specifies the default period that is used when no :days or :seconds
  tag is specified. The configured value must lie between the
  sieve_vacation_min_period and sieve_vacation_max_period.

sieve_vacation_use_original_recipient = no
  This specifies whether the original envelope recipient should be used in
  the check for implicit delivery.  The vacation command checks headers of
  the incoming message, such as To: and Cc: for the address of the
  recipient, to verify that the message is explicitly addressed at the
  recipient. If the recipient address is not found, the vacation action
  will not trigger a response to prevent sending a reply when it is not
  appropriate. Normally only the final recipient address is used in this
  check. This setting allows including the original recipient specified in
  the SMTP session if available. This is useful to handle mail accounts
  with aliases. Use this option with caution: if you are using aliases that
  point to more than a single account, senders can get multiple vacation
  responses for a single message. 
  
sieve_vacation_dont_check_recipient = no
  This disables the checks for implicit delivery entirely. This means that
  the vacation command does not verify that the message is explicitly
  addressed at the recipient. Use this option with caution. Specifying
  'yes' will violate the Sieve standards and can cause vacation replies to
  be sent for messages not directly addressed at the recipient. 

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

Example
=======

plugin {
  # Use vacation-seconds
  sieve_extensions = +vacation-seconds

  # One hour at minimum
  sieve_vacation_min_period = 1h

  # Ten days default
  sieve_vacation_min_period = 10d

  # Thirty days at maximum
  sieve_vacation_max_period = 30d
}