The MIME Message type is used in relation to email and instant messaging. The Internet Assigned Numbers Authority has many registered MIME Message types including:
Each of these MIME Message types has its own use and protocols. For example, CPIM is used for instant messaging while disposition-notification is used to report the disposition of a message after its successful delivery. If you've ever requested a "send receipt," then you've experienced disposition-notification in action.
A notable MIME Message type is rfc822 which defines a message representation protocol covering US-ASCII headers for messages and leaving the message body intact. MIME Message rfc822 defines the entire MIME (Multipurpose Internet Mail Extensions) concept. RFC822 was originally defined in 1982 to standardize the textual format of mail messages on the Internet. It has since been revised to address changes to messaging. According to the Internet Assigned Numbers Authority, the "rfc822" subtype is used when the encapsulated content is itself an RFC 822 message.
How to Open MIME Message
By definition, MIME Message files are mail messages meant to be opened in an email client. As such, your first option is to try opening the file in an email program. For example, you may need to tell your computer how to deal with MIME Message files. This can happen when a file association gets broken. The fix is easy enough to do. First, go to Start and right-click it. Choose Open Windows Explorer and navigate to the MIME Message file that you want to open. Instead of double-clicking it like you normally would do, right-click it and choose Open With > Choose Default Program. Now, browse your computer for your email program such as Microsoft Outlook or Windows Live Mail. Place a checkmark in the box that reads, "Always use this program for this type of file."
MIME Message Associated Applications
Because MIME is a standard dating back to the early 1980s, just about any email client should be able to open a traditional MIME Message. Some of the more popular email clients are listed below:
Microsoft Outlook - Part of the Microsoft Office suite, Microsoft Outlook should not be confused with the free (and discontinued) Microsoft Outlook Express.
Microsoft Outlook Express - No longer offered by Microsoft, Outlook Express remains in use on some older computers.
Windows Mail - Offered for a short time on Windows Vista computers, Microsoft Mail replaced Outlook Express.
Windows Live Mail - Part of Windows Live Essentials, the free Windows Live Mail client is loaded with useful features including a calendar.
Some browsers - Your Web browser may also be able to open your MIME Message including Internet Explorer, Firefox, and Opera.
MIME Message: How to Fix it Quick
Because there are so many MIME Message subtypes addressing various issues, a quick fix isn't always in the cards. If you're merely having trouble opening a MIME email, the file association may be broken. You can reset it in Windows Control Panel > Default Programs > Set Associations tool. Find the file extension related to your MIME message and change the program to your email client.
Below are a few more resources addressing other MIME Message issues.
MIME Plug-in Fix for Windows Embedded CE 6.0 Devices - Microsoft explains how to fix a problem with opening MIME files on Windows Embedded CE 6.0 devices.
Retain MIME Content-Type Header in HTTP Body - Microsoft discusses how to retain MIME content-type headers in HTTP body.
Message Flow Overview - MIME Parsers - Detailed information about MIME Messages from IBM.