Using nullmailer from docker image

use-nullmailer.sh

# this example shows how to run docker container and use nullmailer, running on a host machine

# first, run a container like that

sudo docker run \
  --rm \
  -ti \
  -v `which sendmail`:`which sendmail` \
  -v `which nullmailer-inject`:`which nullmailer-inject` \
  -v `which nullmailer-queue`:`which nullmailer-queue` \
  -v /etc/nullmailer:/etc/nullmailer \
  -v /var/spool/nullmailer:/var/spool/nullmailer \
  ubuntu:trusty \
  bash
  
# and check how sendmail works inside the container

echo "Hello from container" | sendmail somebody@example.com

# it should be put into the /var/spool/nullmailer on the host machine
# and sent by daemon which runs on the host machine

this requires the container to have sendmail installed

I believe ubuntu:trusty had sendmail installed out of the box.

you are right, sorry didn't see the last line
ubuntu:trusty