How to know what Operating Systems have been tested and are supported with a new release of MailStream Plus

Products affected:  MailStream Plus™, all versions
The Operating Systems and  versions tested and supported are listed in the Release Notes that come out with each new release of MailStream Plus™.  
For example:  The 8.3.7 Release Notes includes this on page 23:
Platform-specific information
Release 8.3.7 of MailStream Plus™ is supported on the following platforms:
Platforms          Version
IBM®i              7.2

Linux              RED HAT 6
                   RED HAT 7.X
                   SuSE 11
                   SuSE 12

UNIX               AIX 7.1
                   AIX 7.2
                   SOLARIS 5.10
                   SOLARIS 5.11
                   HP-UX 11.31I

Windows®           2008-R2

z/OS               2.1


Those are the O/S and versions that 8.3.7 has been QA'd on and are supported on.  Although the software may work on other versions due to an Operating Systems' backward and/or forward compatibility, we  cannot  recommend using the product on them, because we cannot guarantee that the product will install, or if it does install that it will work correctly and/or provide correct results.
UPDATED:  May 16, 2019