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_max_subject_codepoints = 256
  The maximum number of Unicode codepoints used in the Subject header generated
  for the outgoing vacation message. When composite characters are involved,
  the number of actual charactes in the Subject text can be less than this
  number, otherwise it is equal. When the subject text exceeds the limit, it is
  truncated and the removed part is replaced with an ellipsis character ('...').

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.

sieve_vacation_send_from_recipient = no
  This setting determines whether vacation messages are sent with the SMTP MAIL
  FROM envelope address set to the recipient address of the Sieve script owner.
  Normally this is set to <>, which is the default as recommended in the
  specification. This is meant to prevent mail loops. However, there are
  situations for which a valid sender address is required and this setting can
  be used to accommodate for those.

sieve_vacation_to_header_ignore_envelope = no
  With this setting disabled (the default), the "To:" header in the composed
  vacation reply is determined by finding the envelope sender address in the
  first "Sender:", "Resent-From:", or "From:" headers (in that order). The
  matching address is used in the "To:" header of the reply, which then includes
  the "phrase" part of the address; i.e., usually the name of the person
  associated with that address. If no match is found, the bare envelope sender
  address is used instead. In contrast, with this setting enabled, the envelope
  is completely ignored for this purpose and the first address found from the
  mentioned headers is always used. This is useful when the envelope sender is
  mangled somehow; e.g. by the Sender Rewriting Scheme (SRS).

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
}

