How to collect bounces in postfix

Question

This is related to this question:

linux - Ways to get a bounceback report for my newsletter application? - Server Fault

Let's say I'm generating email addresses like this when I send out newsletters to identify bounces and unsubscribe them from my newsletter: bounce-123456789@example.com

I assume I'd use this in the return-path, right?

Then how would I set it up in postfix to collect all these addresses prefixed with "bounce-" into one mailbox?

Finally, I've heard people mention a soft bounce vs. a hard bounce. Can someone explain the different and how they should be counted to know when to permanently remove someone from an email newsletter?

Answer 1

The exact answer to your question (handling the bounce-xxx@example.com address) depends on how your server is configured to receive mail. If example.com is the virtual domain the best you can do is collect the messages in the bounce@example.com mailbox (assuming recipient_delimiter = -).

If example.com is the locally delivered domain for the server (mail is delivered to actual system accounts) then you can add a .forward file to the home directory of the bounce user, which delivers to a program that parses the bounce information and records it in a database or file. See man local for more info on the .forward format and how to deliver to a program.

What we do, since we send messages for a large number of domains, is use bounces.example.com as our VERP domain. This domain needs to be added to relay_domains. Create /etc/postfix/transport_maps with this content:

bounces.example.com             bulkbounce:

Then append a line similar to this to /etc/postfix/master.cf:

bulkbounce   unix  -       n       n       -       -       pipe
  user=nobody argv=/usr/local/bin/bounce_handler.py ${recipient}

The bounce_handler.py script accepts the VERP address as its command line option, parses it and makes the necessary database updates to record the bounce.

Answer 2

Actually, Instyle's answer is very difficult to implement if you want to support many different domains and it is wrong because:

a) With his example of transport_maps, all the emails sent to that domain are sent to that specific service without any regard to whether the emails are bounced emails or not. Since it uses a specific domain name, it should indeed only be bounced emails... but it cannot be guaranteed that way.

b) The data sent to your script is the email itself and not the bounce message. In other words, your code may have no idea why the email was bounced (i.e. local bounce will send you the original email only.)

---

The correct way to do that setup in postfix is to use the bounce notification class.

1) In /etc/postfix/main.cf

notify_classes = bounce
bounce_notice_recipient = bounces@example.com
transport_maps = hash:/etc/postfix/transport_maps

2) In /etc/postfix/transport_maps

# when you make changes to this file, run:
#   sudo postmap /etc/postfix/transport_maps
bounces@example.com bulkbounce:

As you can see, we now tell postfix to use bounces@example.com whenever an email gets bounced. Then in the transport map, to use bulkbounce as the service to handle any email address to bounces@example.com.

Finally you can define bulkbounce with your script:

3) In /etc/postfix/master.cf

bulkbounce unix -       n       n       -       -       pipe
  flags=FRq user=bounce argv=/home/bounce/bin/snapbounce --sender ${sender} --recipient ${recipient}

This script requires you to have a user. nobody is a good choice too. If you want to have a specific user, you can create it with:

useradd bounce

Without the script in master.cf, the emails are sent to the bulkbounce account. So if you have a script that parses emails from files, this would work without the transport_maps and master.cf changes.

---

From a comment below:

fyi - re: double bounces...
if you're modifying the return address (VERP address such as user+id@fromdomain.com, then you will want to comment out the line in main.cf for the bounce_notice_recipient, if you're interested in parsing the +id bounce only in your script.

Answer 3

Most modern mailing list software already knows how to handle VERP messages if the MTA is properly configured to pass them back to the mailing list software. In the case of GNU Mailman you should checkout the FAQ page aptly named "How do I use VERP with a - delimiter (Postfix recipient_delimiter)?".

If you're making your own custom newsletter software to handle this you should ask yourself why you're re-inventing the wheel instead of using existing applications that can handle the task simply and easily for you already.