filter software package provides program that filters local email via forward/pipe, 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 filter
filter is installed in your system.
Make ensure the filter package were installed using the commands given below,
$ sudo dpkg-query -l | grep filter *
You will get with filter package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | |
| Package | filter |
| Version | 2.6.3+ds1-3 |
| Description | program that filters local email via forward/pipe |
| Sub Section |