Redhat has chosen userid 51 for their SMMSP user for Sendmail.  Furthermore, our use of the UserID 102 is 
merely a standard we use.

There is no requirement for the number beyond understanding that it should be unique on YOUR system.

If you wish to mimic RedHat 8.0's user id, you will want to use the following lines to create your SMMSP user:

/usr/sbin/groupadd -r -g 51 smmsp
/usr/sbin/adduser -M -u 51 -s /bin/false -g smmsp smmsp


Additionally, while we strongly recommend doing a rpm -e sendmail, some people do not feel comfortable doing
so.  If you do not erase the sendmail RPM, the default RedHat permissions on /var/spool/clientmqueue may be
incompatible with Sendmail's security requirements.  This can be fixed by running the following commands:

chown smmsp.smmsp /var/spool/clientmqueue
chmod 770 /var/spool/clientmqueue


Thanks to Greg Smith for his input!