You need a working sendmail command for email alerts to work. Almost all MTAs provide a sendmail interface.
netdata sends all emails as user netdata, so make sure your sendmail works for local users.
email notifications look like this:
To edit health_alarm_notify.conf on your system run /etc/netdata/edit-config health_alarm_notify.conf.
You can configure recipients in /etc/netdata/health_alarm_notify.conf.
You can also configure per role recipients in the same file, a few lines below.
Changes to this file do not require netdata restart.
You can test your configuration by issuing the commands:
# become user netdata
sudo su -s /bin/bash netdata
# send a test alarm
/usr/libexec/netdata/plugins.d/alarm-notify.sh test [ROLE]Where [ROLE] is the role you want to test. The default (if you don't give a [ROLE]) is sysadmin.
Note that in versions before 1.16, the plugins.d directory may be installed in a different location in certain OSs (e.g. under /usr/lib/netdata). You can always find the location of the alarm-notify.sh script in netdata.conf.