SMTP connectivity issue in Zenoss ("Connection unexpectedly closed")

I am using Zenoss for monitoring purpose. I have been using its mail service for a long time. Suddenly my mail service in zenoss stopped and started showing - Connection unexpectedly closed and no mails are outgoing. When I ran the mail command via CLI, the mail goes to the email address. While executing the zenoss script for mailer won't work and throws out the error as shown above. My server is RHEL 5.3 x86_64, with Zenoss 4.2 & sendmail email server. ### Sendmail logs & Zenoss email conf Apr 11 07:14:30 XXXhostnameXX sendmail: r3BBDgia013582: lost input channel from localhost.localdomain [127.0.0.1] to MTA after mail Apr 11 07:14:30 XXXhostnameXX sendmail: r3BBDgia013582: from=, size=146972, class=0, nrcpts=0, proto=ESMTP, daemon=MTA, relay=localhost.localdomain [127.0.0.1] Zenoss is following basic smtp connection as emailing is done by local sendmail server (localhost) in port 25. No specific configuration is used.