History: Email bounce handling

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New in ((Tiki25)). Leveraging [https://packagist.org/packages/rambomst/php-bounce-handler|rambomst/php-bounce-handler] and ((Email filters)), handle email bounces in Tiki: add system tracker to hold bounce information, add bounce handler lib, add sieve filters to check for bounces and add to bounce list in ((system trackers)).


Initial commit: https://gitlab.com/tikiwiki/tiki/-/merge_requests/1879

!!What is bounce
A bounced email, or bounce, is an email message that gets rejected by a mail server. When an email bounces, it has for some reason not reached the intended destination.

A bounced email can be either a hard bounce or a soft bounce. A hard bounce means that the email address is permanently unavailable and should not receive electronic mail. A soft bounce is temporary, and may be caused by server outages or a full inbox. Most email service providers will designate soft bounces as a hard bounce after three failed sends.

!!How to configure
!!!Step 1: Configure system tracker holding bounce information

Go to [System-Trackers], access it from /tiki-admin.php?page=trackers and check __Email bounces tracker__ then:

* Choose which tracker will store the bounced emails and statistics.
* Choose an email field that stores the email address that bounced.
* Choose an email folder field that stores the bounced messages read by Tiki.
* Choose a numeric field that stores the total number of soft bounces occured for an email address.
* Choose a numeric field that stores the total number of hard bounces occured for an email address.
* Choose a checkbox field that stores the blacklist state for an email address - whether Tiki should skip sending emails to that email address or not.

{img attId=179 width="800" align="center" desc="click to enlarge" title="System tracker configuration"}

^Create a tracker  with these fields before^

{img attId=181 width="800" align="center" desc="click to enlarge" title="Fields require for bounce system tracker"}

!!!Step 2: Configure the filter
Go to [Webmail], Click on __filters__ in settings section then click on __add filter__ and set other details of filter: name, priority and test. In the conditions & actions section, Add __is bounce__ as a condition and select __type__ of condition soft, is not soft, hard, not hard. Then click on add action and pick __add to bounce list__

{img attId=180 width="800" align="center" desc="click to enlarge" title="Bounce filter configuration"}

!!!Step 3: Set up cron job

Finally add __php console.php sieve:filters__ command to Tiki Scheduler or a cron job

When these are configured and condition is met (using https://github.com/rambomst/PHP-Bounce-Handler/) item is created/updated in the bounce tracker, updating soft/hard bounce counts, the email added to the tracker email field (if configured)