I'm very new to Nagios. I'm trying to send email alerts. But that doesn't seem to be working.

But in my log of nagios I can see this :

SERVICE ALERT: Appserver;Tmp directory;CRITICAL;HARD;1;

Where host notifications are generated via email, only service alerts are not working. And when I look at sendEmail log I can see this :

Sep 14 12:38:39 x.x.x.x. sendEmail[23005]: ERROR => You must specify a 'from' field!  Try --help.
Sep 14 12:39:39 x.x.x.x.x. sendEmail[23129]: ERROR => You must specify a 'from' field!  Try --help.
Sep 14 12:40:39 x-x-x-x-x sendEmail[23233]: ERROR => You must specify a 'from' field!  Try --help.

Where I'm making the mistake?

Thanks in advance.