SAPMSHOST is a SAP Parameter attribute which is used to control Hostname where message server is located information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
This parameter specifies the host on which the message server runs.
This entry must be the same on all application servers belonging to one
SAP system and for this reason it is to be set only in the default
profile.
The name of the host must be known in the host database.
UNIX
Must be entered in the /etc/hosts file or on the domain name server.
Microsoft Windows
Must be entered in the file C:\WINNT\SYSTEM32\DRIVERS\ETC\HOSTS or on
the domain name server.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.