To enable the [fetchmail](http://www.fetchmail.info) service to retrieve e-mails set the environment variable `ENABLE_FETCHMAIL` to `1`. Your `docker-compose.yml` file should look like following snippet:
A detailed description of the configuration options can be found in the [online version of the manual page](http://www.fetchmail.info/fetchmail-man.html).
More details how to configure fetchmail can be found in the [fetchmail man page in the chapter “The run control file”](http://www.fetchmail.info/fetchmail-man.html#31).