There's few way to restart you sendmail in AIX.

1. # refresh -s sendmail
2. # sendmail -bi
3. # sendmail.cf stop 
   # sendmail.cf start
4. # stopsrc -s sendmail 
   # startsrc -s sendmail

If you discover that the sendmail daemon dies after you started it. You have to pass the parameters to sendmail to start it correctly. So best would be:

# stopsrc -s sendmail
# startsrc -s sendmail -a"-bd -q30m"

If you only need to refresh the configuration you can also run:

# refresh -s sendmail