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Subsections

- 23.1 VERP

# 23. 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 (note that the -owner suffix can be customized, see 7.8.4, page ), which should be sent to the `bouncequeue` program via aliases :

    	\samplelist-owner: "|/usr/local/sympa-stable/bin/bouncequeue \samplelist"

`bouncequeue` (see 2.2, page ) stores bounces in a `/usr/local/sympa-stable/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 7.8.9, page )

  - The bouncing period is shorter than `minimum_bouncing_period` (see 7.8.10, page )

- You can define the limit between each level via the List configuration pannel, in subsection Bounce settings. (see 20.5.2) 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 20.5.2) Each time an action will be done, a notification email will be send to the person of your choice. (see 20.5.2)

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23.1 VERP

VERP (Variable Envelop Return Path) is used to ease automatic recognition of subscribers email address when receiving a bounce. If VERP is enabled, the subscriber address is encoded in the return path itself so Sympa bounce management processus (bounced) will use the address the bounce was received for to retreive the subscriber email. This is very usefull because sometimes, non delivery report don't contain the initial subscriber email address but an alternative address where messages are forwarded. VERP is the only solution to detect automaticaly these subscriber errors but the cost of VERP is significant, indeed VERP requires to distribute a separate message for each subscriber and break the bulk emailer grouping optimization.

In order to benefit from VERP and keep distribution process fast, Sympa enables VERP only for a share of the list members. If texttt `verp_rate` (see 7.8.1,page ) is 10% then after 10 messages distributed in the list all subscribers have received at least one message where VERP was enabled. Later distribution message enable VERP also for all users where some bounce wer collected and analysed by previous VERP mechanism.

Next: 24. Antivirus Up: Sympa Mailing Lists Management Software version Previous: 22. Shared documents Contents Index