The CIO of Bigcompany.com (a fictitious company for my purposes) has presented you, the Messaging Director, with two challenges.
First, your company must be able to send e-mail in Asian languages—especially Japanese—to your Far East affiliates (so the characters appear properly: Ï̵"뢣 ¥¢¥µ¥Ò).
Second, your company's employees are upsetting users of various Internet mailing lists because their messages to the list are encoded in HTML. Mailing lists and mail software packages don't handle HTML gracefully. When HTML-encoded mail arrives, HTML tags appear alongside the text, making it difficult for people to read the message. Although your fellow employees can manually set each mailing list reply in plain text, it's tedious and they often forget to do it.
The CIO wants you to fix this problem so that messages that employees send to mailing lists from the office will be in plain text only, while messages they send elsewhere will retain the advantages of HTML encoding.

How do you send HTML-formatted e-mail to some users, while keeping e-mail in plain-text format for others?

The Exchange 5.5 Internet Mail Service is more than just a dumb conduit—it influences greatly how your messages look when they're delivered and determines the domains from which your inbound mail is received. By configuring the IMS to send certain formats to specific domains, you can ensure that it will only allow plain-text messages to be sent to certain domains, while still allowing HTML-encoded messages to go to other domains.