Notice also that within the Internet cloud there are other people connecting to send and receive their email. When they dialup, they typically use two other mail Protocols, POP and IMAP to retrieve their mail from an email server. Viruses - I am sure that you are all more or less aware of the threat that viruses pose to your Organization's. Several of the recent virus outbreaks have made the news and we've all heard the stories of doom and gloom from those affected by the outbreaks. Trojan horses - so named because like the Trojan horse of Troy, they contain within them something that you aren't expecting.
Someone receives an executable file, clicks on it and the rest is history.
Lots of Spam. Spam is typically junk email. This can cost your organization quite a lot of bandwidth, and as we know bandwidth and ISP volume charges add up to a lot of money. This can be mildly annoying, or highly offensive depending on the content of the mail. How are they using your email system.