this is not about server sendmail client, your mail server not listenening smtp or firewall not allow to access, first try to telnet localhost 25 on smtp server, if ok check your firewall rule, if...
Aix6.1, 04 technology level, 01 maintenance level (servicepack)
you can find latest level on following link,
http: www-933.ibm. com/support/fixcentral/