Hi there,
Need assistance on this. I've been trying to make my email notification service to work in Nagios but to no avail.

Please check configs if I am missing something:

Contactgroup.cfg:
define contactgroup{
contactgroup_name administrators
alias Administrators
members user1,user2
}

Contacts.cfg:
#define contact{
# contact_name nagios-admin
# alias Nagios Admin
# service_notification_period 24x7
# host_notification_period 24x7
# service_notification_options w,u,c,r
# host_notification_options d,r
# service_notification_commands notify-by-email
# host_notification_commands host-notify-by-email
# email nagios-admin@localhost
# }

define contact{
contact_name user1
alias User1
service_notification_period 24x7
host_notification_period 24x7
service_notification_options w,u,c,r
host_notification_options d,r
service_notification_commands notify-by-email
host_notification_commands host-notify-by-email
email user1@domain.com
}
define contact{
contact_name user2
alias User2
service_notification_period 24x7
host_notification_period 24x7
service_notification_options w,u,c,r
host_notification_options d,r
service_notification_commands notify-by-email
host_notification_commands host-notify-by-email
email user2@domain.com
}

This is where I followed the instructions from:
http://nagios.sourceforge.net/docs/3...rt-ubuntu.html

I have verified my configs, Things look okay - No serious problems were detected during the pre-flight check.

Please advise, thnx in advance!

contacts.cfg and contactgroup.cfg seems ok

check below mention things somewhere in your cfg file if it is not available add this in checkcommand.cfg or where you have added nagios addons

###############################################################################
#
# SAMPLE NOTIFICATION COMMANDS
#
# These are some example notification commands. They may or may not work on
# your system without modification. As an example, some systems will require
# you to use "/usr/bin/mailx" instead of "/usr/bin/mail" in the commands below.
#
################################################################################


# 'host-notify-by-email' command definition
define command{
command_name host-notify-by-email
command_line /usr/bin/printf "%b" "***** Nagios 2.9 *****\n\nNotification Type: $NOTIFICATIONTYPE$\nHost: $HOSTNAME$\nState: $HOSTSTATE$\nAddress: $HOSTADDRESS$\nInfo: $HOSTOUTPUT$\n\nDate/Time: $LONGDATETIME$\n" | /bin/mail -s "Host $HOSTSTATE$ alert for $HOSTNAME$!" $CONTACTEMAIL$
}


# 'host-notify-by-epager' command definition
define command{
command_name host-notify-by-epager
command_line /usr/bin/printf "%b" "Host '$HOSTALIAS$' is $HOSTSTATE$\nInfo: $HOSTOUTPUT$\nTime: $LONGDATETIME$" | /bin/mail -s "$NOTIFICATIONTYPE$ alert - Host $HOSTNAME$ is $HOSTSTATE$" $CONTACTPAGER$
}

# 'notify-by-email' command definition
define command{
command_name notify-by-email
command_line /usr/bin/printf "%b" "***** Nagios 2.9 *****\n\nNotification Type: $NOTIFICATIONTYPE$\n\nService: $SERVICEDESC$\nHost: $HOSTALIAS$\nAddress: $HOSTADDRESS$\nState: $SERVICESTATE$\n\nDate/Time: $LONGDATETIME$\n\nAdditional Info:\n\n$SERVICEOUTPUT$" | /bin/mail -s "** $NOTIFICATIONTYPE$ alert - $HOSTALIAS$/$SERVICEDESC$ is $SERVICESTATE$ **" $CONTACTEMAIL$
}


# 'notify-by-epager' command definition
define command{
command_name notify-by-epager
command_line /usr/bin/printf "%b" "Service: $SERVICEDESC$\nHost: $HOSTNAME$\nAddress: $HOSTADDRESS$\nState: $SERVICESTATE$\nInfo: $SERVICEOUTPUT$\nDate: $LONGDATETIME$" | /bin/mail -s "$NOTIFICATIONTYPE$: $HOSTALIAS$/$SERVICEDESC$ is $SERVICESTATE$" $CONTACTPAGER$
}

I checked my commands.cfg and saw the exact same script you have above.
Anything else I am missing or need to do?

Thanks for your assistance!

Here's my config:

################################################################################
#
# SAMPLE NOTIFICATION COMMANDS
#
# These are some example notification commands. They may or may not work on
# your system without modification. As an example, some systems will require
# you to use "/usr/bin/mailx" instead of "/usr/bin/mail" in the commands below.
#
################################################################################


# 'host-notify-by-email' command definition
define command{
command_name host-notify-by-email
command_line /usr/bin/printf "%b" "***** Nagios 2.10 *****\n\nNotification Type: $NOTIFICATIONTYPE$\nHost: $HOSTNAME$\nState: $HOSTSTATE$\nAddress: $HOSTADDRESS$\nInfo: $HOSTOUTPUT$\n\nDate/Time: $LONGDATETIME$\n" | /bin/mail -s "Host $HOSTSTATE$ alert for $HOSTNAME$!" $CONTACTEMAIL$
}


# 'host-notify-by-epager' command definition
define command{
command_name host-notify-by-epager
command_line /usr/bin/printf "%b" "Host '$HOSTALIAS$' is $HOSTSTATE$\nInfo: $HOSTOUTPUT$\nTime: $LONGDATETIME$" | /bin/mail -s "$NOTIFICATIONTYPE$ alert - Host $HOSTNAME$ is $HOSTSTATE$" $CONTACTPAGER$
}

# 'notify-by-email' command definition
define command{
command_name notify-by-email
command_line /usr/bin/printf "%b" "***** Nagios 2.10 *****\n\nNotification Type: $NOTIFICATIONTYPE$\n\nService: $SERVICEDESC$\nHost: $HOSTALIAS$\nAddress: $HOSTADDRESS$\nState: $SERVICESTATE$\n\nDate/Time: $LONGDATETIME$\n\nAdditional Info:\n\n$SERVICEOUTPUT$" | /bin/mail -s "** $NOTIFICATIONTYPE$ alert - $HOSTALIAS$/$SERVICEDESC$ is $SERVICESTATE$ **" $CONTACTEMAIL$
}


# 'notify-by-epager' command definition
define command{
command_name notify-by-epager
command_line /usr/bin/printf "%b" "Service: $SERVICEDESC$\nHost: $HOSTNAME$\nAddress: $HOSTADDRESS$\nState: $SERVICESTATE$\nInfo: $SERVICEOUTPUT$\nDate: $LONGDATETIME$" | /bin/mail -s "$NOTIFICATIONTYPE$: $HOSTALIAS$/$SERVICEDESC$ is $SERVICESTATE$" $CONTACTPAGER$

Can you successfully send mail from the command line using /bin/mail..?

Yes I can send mail when sending a test in the box, no issues there. Thanks for checking!

UPDATE:
I verified the scripts and such then tested it once again, now getting this from my message logs:
Apr 1 16:46:16 srv nagios: HOST NOTIFICATION: user1;server.domain.com;DOWN;host-notify-by-email;PING CRITICAL - Packet loss = 100%
Apr 1 16:46:16 srv nagios: Warning: Attempting to execute the command "/usr/bin/printf "%b" "***** Nagios 2.10 *****\n\nNotification Type: PROBLEM\nHost: server.domain.com\nState: DOWN\nAddress: 172.168.1.25\nInfo: PING CRITICAL - Packet loss = 100%\n\nDate/Time: Wed Apr 1 16:46:16 PDT 2009\n" | /bin/mail -s "Host DOWN alert for server.domain.com!" user1@domain.com" resulted in a return code of 127. Make sure the script or binary you are trying to execute actually exists...

I made sure that there are no quoting errors causing my problem which I checked my command definition
for host-notify-by-email.

################################################################################
#
# SAMPLE NOTIFICATION COMMANDS
#
# These are some example notification commands. They may or may not work on
# your system without modification. As an example, some systems will require
# you to use "/usr/bin/mailx" instead of "/usr/bin/mail" in the commands below.
#
################################################################################


# 'host-notify-by-email' command definition
define command{
command_name host-notify-by-email
command_line /usr/bin/printf "%b" "***** Nagios 2.10 *****\n\nNotification Type: $NOTIFICATIONTYPE$\nHost: $HOSTNAME$\nState: $HOSTSTATE$\nAddress: $HOSTADDRESS$\nInfo: $HOSTOUTPUT$\n\nDate/Time: $LONGDATETIME$\n" | /bin/mail -s "Host $HOSTSTATE$ alert for $HOSTNAME$!" $CONTACTEMAIL$
}

# 'host-notify-by-epager' command definition
define command{
command_name host-notify-by-epager
command_line /usr/bin/printf "%b" "Host '$HOSTALIAS$' is $HOSTSTATE$\nInfo: $HOSTOUTPUT$\nTime: $LONGDATETIME$" | /bin/mail -s "$NOTIFICATIONTYPE$ alert - Host $HOSTNAME$ is $HOSTSTATE$" $CONTACTPAGER$
}

# 'notify-by-email' command definition
define command{
command_name notify-by-email
command_line /usr/bin/printf "%b" "***** Nagios 2.10 *****\n\nNotification Type: $NOTIFICATIONTYPE$\n\nService: $SERVICEDESC$\nHost: $HOSTALIAS$\nAddress: $HOSTADDRESS$\nState: $SERVICESTATE$\n\nDate/Time: $LONGDATETIME$\n\nAdditional Info:\n\n$SERVICEOUTPUT$" | /bin/mail -s "** $NOTIFICATIONTYPE$ alert - $HOSTALIAS$/$SERVICEDESC$ is $SERVICESTATE$ **" $CONTACTEMAIL$
}

# 'notify-by-epager' command definition
define command{
command_name notify-by-epager
command_line /usr/bin/printf "%b" "Service: $SERVICEDESC$\nHost: $HOSTNAME$\nAddress: $HOSTADDRESS$\nState: $SERVICESTATE$\nInfo: $SERVICEOUTPUT$\nDate: $LONGDATETIME$" | /bin/mail -s "$NOTIFICATIONTYPE$: $HOSTALIAS$/$SERVICEDESC$ is $SERVICESTATE$" $CONTACTPAGER$
}


Is there anything that you see or know that I must do/correct in the above statement? Please advise, desperately need assistance to make this work. Thanks in advance!