1. In shell, type mailq
You can see how many emails are queued.
Or manually check:
2. in shell, not in SU mode, type pine
You will see all the bounce back emails.
Helps determine if your server is being used as a spamming source. You can also delete all the bouncebacks/
3. Check your /var parition being typing df in shell.
You do not need to reboot the server to restart sendmail on Raqs.
You can restart all the useful goodies in /etc/rc.d/init.d/
PM me if you want me to take a look.