DEV Community

Yaroslav Polyakov
Yaroslav Polyakov

Posted on • Edited on

1

Drop [almost] all outbound mail in postfix for tests

Why to drop mail?

While troubleshooting mailman installation, I've come to a problem: I need to do many tests, but I do not want to disturb recipients of maillist with dozens of test messages. I do not know, if mailman3 has any feature for this kind of testing, but postfix has.

How to drop postfix mail except to whitelisted addresses

First, make sure, you have transport map enabled.

Usually, this line could look like this:

transport_maps = hash:/etc/postfix/transport
Enter fullscreen mode Exit fullscreen mode

Now, create other transport file, my /etc/postfix/blackhole:

mydomain.net :
mymailbox@gmail.com :
* discard:
Enter fullscreen mode Exit fullscreen mode

With this config postfix will deliver to *@mydomain.net and to mymailbox@gmail.com.

run postmap blackhole to generate /etc/postfix/blackhole.db.

add it to postfix transport with comma (if you already has transport map):

transport_maps = hash:/path/to/other/transport/map, hash:/etc/postfix/blackhole
Enter fullscreen mode Exit fullscreen mode

(or as single element, if you had no transport_maps).

Restart postfix: postfix reload. You're ready.

Testing

I sent few mails and here is what I have in logs:

Jan 12 09:53:17 list2 postfix/smtp[62239]: DB97418C0808: to=<mymailbox@gmail.com>, relay=gmail-smtp-in.l.google.com[173.194.76.27]:25, delay=0.41, delays=0.03/0.02/0.14/0.22, dsn=2.0.0, status=sent (250 2.0.0 OK  1673517197 g15-20020a056000118f00b002bdd88acc3dsi514695wrx.503 - gsmtp)

Jan 12 09:53:34 list2 postfix/discard[62251]: 7943118C0808: to=<test@test.com>, relay=none, delay=0.02, delays=0.02/0/0/0, dsn=2.0.0, status=sent (test.com)
Enter fullscreen mode Exit fullscreen mode

First is log line for real delivery (relay= remote mailserver) and second is log line for blackhole delivery, relay=none).

Do your career a big favor. Join DEV. (The website you're on right now)

It takes one minute, it's free, and is worth it for your career.

Get started

Community matters

Top comments (0)

A Workflow Copilot. Tailored to You.

Pieces.app image

Our desktop app, with its intelligent copilot, streamlines coding by generating snippets, extracting code from screenshots, and accelerating problem-solving.

Read the docs

👋 Kindness is contagious

Dive into an ocean of knowledge with this thought-provoking post, revered deeply within the supportive DEV Community. Developers of all levels are welcome to join and enhance our collective intelligence.

Saying a simple "thank you" can brighten someone's day. Share your gratitude in the comments below!

On DEV, sharing ideas eases our path and fortifies our community connections. Found this helpful? Sending a quick thanks to the author can be profoundly valued.

Okay