postfix after queue not working

Question

I'm trying to play with the postfix after queue. Basically, I want to see if I can modify outgoing email. (I'm not interested at all in incoming email). I did the following (based on http://www.postfix.org/FILTER_README.html) :

1. launch ec2 on aws (ubuntu 16.04)
2. install postfix
3. created filter with user filter

4. modify the master.cf by adding the -o content_filter=filter:dummy

   smtp inet n - y - - smtpd -o content_filter=filter:dummy

5. add the filter service definition at the end of the master.cf file

   filter unix - n n - 10 pipe flags=Rq user=filter null_sender= argv=/home/ubuntu/run_filter.sh -f ${sender} -- ${recipient}

6. Send email using

   echo "hello world" | mail -s "second message" [email protected]

But the filter is not called. And the email is sent without any change.

It seems like I'm missing something very basic. If someone can help, thanks!

Answer 1

It could be that your php.ini isn't referencing the correct path to sendmail.

You can check your php.ini file or apache logs to confirm this.

Alternatively, you can use the absolute path instead:

echo "Subject: test" | /usr/sbin/sendmail [email protected] 

you can also confirm the registered path from command line:

which sendmail 

Good Luck :)

Answer 2

I may be wrong as I don't know exactly your setup, but I think that mail does not send messages through smtp. You can check postfix logs, if your message is received via postfix/smtpd or via postfix/pickup.

You can configure mail to use smtp I think, depends what mail you have installed (mailx, nail etc).

Answer 3

This answer doesn't answer directly your question, but could help you more on long term.

When I have an application that I expect to do something, I am using tracing tools like strace, tcpdump/wireshark, perf, systemtap.

In your case, because I expect mail to connect via a TCP or at least an Unix socket to send the email, I would run it under strace.

echo "hello world" | strace -f -e network mail -s "second message" [email protected] 

-f = follow child processes too.

-e network = trace only network related system calls. You may use -e file to see which files are used. For more details see strace(1) man page