/etc/courier/module.esmtp is in courier-mta 0.73.1-1.6.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6
NAME=esmtp PRIORITY=50 PROG=./courieresmtp MAXDELS=40 MAXHOST=4 MAXRCPT=100