Importance of Monitoring Emails within an Organisation
Sensitive information today is crucial in ensuring it is kept safe and secure from external threats. There are different types of email threats. Company asset threat is a type of threat when someone from outside of the company is posing as an authorised user and gains confidential data not available to un-authorised users. This can also be seen as sensitive information being released by a user from inside the company to users outside the company. Sending and receiving personal, none business related email is another type of threat; such as sending and receiving of pornography, abuse, and other generally none related business email and immorally un ethically correct.
Usually, with having an email monitoring system in place reduces the risks of employees abusing the system. Internal staff will think twice about not sending each other inappropriate material if they knew emails were being monitored and stored for legal reasons.
Whatever the threat, it is crucial a system is put into place, which monitors and protects against such threats, and employees are made aware emails are secure and monitored for various reasons in line with the organisation security policies. A good anti-spam firewall providing granular reporting and ability to track historic email messages is required for these reasons.
Further Reading
Wikipedia's guide to Email Tracking