Hi,
I run openproject in a docker container. Since I want to be able to configure openproject from outside the container I start it as follows, using a configuration file:

docker run -d -p 80:80 --name openproject 
   --env-file /home/openproject/configuration.env 
   -v /home/openproject/pgdata:/var/lib/postgresql/9.4/main 
   -v /home/openproject/logs:/var/log/supervisor 
   -v /home/openproject/static:/var/db/openproject openproject/community:5.0

My /home/openproject/configuration.env file looks as follows:

SECRET_KEY_BASE=secret
EMAIL_DELIVERY_METHOD=sendmail
SENDMAIL_LOCATION=/usr/sbin/sendmail

When I log in as admin and go to Administration -> System Settings -> Email Notification and click on Send a test email, I get the popup containing this message: An email was sent to myemail.de@

Tailing the /home/openproject/logs/web-stdout.log log reveals this message after sending the test mail:

App 396 stdout: Sent mail to my@email.de (33.6ms)
App 396 stdout: Redirected to http://153.96.234.121/settings/edit?tab=notifications
App 396 stdout: Completed 302 Found in 322ms (ActiveRecord: 1.5ms)
App 396 stdout: Started GET "/settings/edit?tab=notifications" for 127.0.0.1 at 2016-06-27 09:27:49 +0000
App 396 stdout: Processing by SettingsController#edit as HTML
App 396 stdout:   Parameters: {"tab"=>"notifications"}

But the problem is, that I never get an email in my mailbox. Can you please help me how to solve this? Is the openproject docker image not configured correctly for sendmail? Any hints, which log might be relevant to solve this?