Message body is garbled when email is received by Microsoft Exchange server

This is a known Microsoft issue caused by the email message format. When the email message uses different encoding in email header and different encoding in email body, the message body becomes garbled because Outlook uses header encoding to parse the entire email message. This can also happen when the message body contains multiple parts each using different encoding (character set). More details can be found in following Microsoft's knowledge base article:

The body of an e-mail message is garbled when the message is viewed in Outlook in an Exchange Server 2003 organization