All of the startup/shutdown typically reside in /etc/init.d and are symlinked to the appropriate level where they are started/stopped. To start sendmail, you would use:
To prevent a service from being started, find the run level where is get started and remove or rename the script so that is does not start with capital S. For example, to disable sendmail startup:
mv S88sendmail nostart_S88sendmail
Most applications in Solaris are started/stopped at only one run level because Solaris progresses though the intermediate run levels when it changes run level. For example, when a system boots, the system runs each S## script in /etc/rc1.d, then each S## script in /etc/rc2.d, then each S## in /etc/rc3.d. When it shuts down, it will run the K## scripts at each run level (3,2,1,0).