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# 16. Bounce management

Sympa allows bounce (non-delivery report) management. This prevents list owners from receiving each bounce (1 per message sent to a bouncing subscriber) in their own mailbox. Without automatic processing of bounces, list owners either go mad, or just delete them without further attention.

Bounces are received at mylist-owner address, which should be sent to the `bouncequeue` program via aliases :

    	\samplelist-owner: "|/home/sympa/bin/bouncequeue \samplelist"

`bouncequeue` (see 2.2, page ) stores bounces in a `/home/sympa/spool/bounce/` spool.

Bounces are then processed by the `bounced.pl` daemon. This daemon analyses bounces to find out which e-mail addresses are concerned and what kind of error was generated. If bouncing addresses match a subscriber's address, information is stored in the Sympa database (in subscriber_table). Moreover, the most recent bounce itself is archived in `bounce_path/mylist/email` (where bounce_path is defined in a `wwsympa.conf` parameter and email is the user e-mail address).

When reviewing a list, bouncing addresses are tagged as bouncing. You may access further information such as dates of first and last bounces, number of received bounces for the address, the last bounce itself.

With these informations, the automatic bounce management is possible:

- The automatic task `eval_bouncer` gives a score foreach bouncing user. The score, between 0 to 100, allows the classification of bouncing users in two levels. (Level 1 or 2). According to the level, automatic actions are executed periodicaly by `process_bouncers` task.

- The score evaluation main parameters are:

  `Bounces count`: The number of bouncing messages received by sympa for the user.

  `Type rate` : Bounces are classified depending on the type of errors generated on the user side. If the error type is "mailbox is full" (ie a temporary 4.2.2 error type) the type rate will be 0.5 whereas permanent errors (5.x.x) have a type rate equal to 1.

  `Regularity rate` : This rate tells if the bounces where received regularly, compared to list traffic. The list traffic is deduced from `msg_count` file data.

            The score formula is  :

            Score = bounce_count * type_rate * regularity_rate

  To avoid making decisions (ie defining a score) without enough relevant data, the score is not evaluated if :

  - The number of the number of received bounces is lower than `minimum_bouncing_count` (see 5.8.9, page )

  - The bouncing period is shorter than `minimum_bouncing_period` (see 5.8.10, page )

- You can define the limit between each level via the List configuration pannel, in subsection Bounce settings. (see 14.5.2) The principle consists in associating a score interval with a level.

- You can also define wich action must be applied on each category of user.(see 14.5.2) Each time an action will be done, a notification email will be send to the person of your choice. (see 14.5.2)

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