https://docs.oracle.com/cd/E23824_01/html/821-1454/mailadmin-13.html#scrolltoc

Add a flag in the script to make the script run on Solaris or Linux, For solaris use the native Sendmail functionality

pkg info sendmail
Name: service/network/smtp/sendmail
Summary: Sendmail
Description: Sendmail Utilities
Category: System/Core
State: Installed
Publisher: pluribusnetworks.com
Version: 8.14.4
Build Release: 5.11
Branch: 2050212426
Packaging Date: November 21, 2016 03:29:30 PM
Size: 3.43 MB
FMRI: pkg://pluribusnetworks.com/service/network/smtp/[email protected],5.11-2050212426:20161121T152930Z