When configuring the Email subsystem for delivery of Email
notifications, at the very least the To (or CC) and
From fields must be configured.
For testing purposes you can send a Email immediately by pressing
the Send Email button.
The Overriding Domain is used to forge the sender Domain Name
in the outgoing Email message. This might be necessary, for example,
if this device is located behind a firewall whose IP Address resolves
to a different Domain Name than this device. For SPAM protection,
many SMTP servers perform reverse lookups on the sender IP Address to
ensure the Email message is really from who it says it's from.