Install sqlgrey by entering the following commands in the terminal:
sudo apt update sudo apt install sqlgrey
Description:
Postfix Greylisting Policy Server
A policy server for Postfix implementing greylisting. . Could be configured to use MySQL, PostgreSQL or SQLite. PostgreSQL is recommended by author.
Homepage: http://sqlgrey.sourceforge.net/
Version: 1:1.8.0-1
Section: universe/mail