I am writing a C# application which allows users to store emails in a MS SQL Server database. Many times, multiple users will be copied on an email from a customer. If they all try to add the same email to the database, I want to make sure that the email is only added once.

MD5 springs to mind as a way to do this. I don't need to worry about malicious tampering, only to make sure that the same email will map to the same hash and that no two emails with different content will map to the same hash.

My question really boils down to how one would combine multiple fields into one MD5 (or other) hash value. Some of these fields will have a single value per email (e.g. subject, body, sender email address) while others will have multiple values (varying numbers of attachments, recipients). I want to develop a way of uniquely identifying an email that will be platform and language independent (not based on serialization). Any advice?