courier-authdaemon software package provides Courier authentication daemon, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install courier-authdaemon
courier-authdaemon is installed in your system.
Make ensure the courier-authdaemon package were installed using the commands given below,
$ sudo dpkg-query -l | grep courier-authdaemon *
You will get with courier-authdaemon package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | |
| Package | courier-authdaemon |
| Version | 0.66.4-7 |
| Description | Courier authentication daemon |
| Sub Section |