Incoming e-mails processed by our mail server sometimes suffer from the following problem: When you receive a message, you might see strange and unexpected attachments with confusing names like “mime-attachment.txt”. In many cases, the text of the message appears to be crippled, scattered over the attachments.

This is due to an incompatibility (bug?) of the institute’s e-mail server, which doesn’t understand inline attachments in non-HTML e-mails. Instead of leaving them alone, the server inserts additional control statements into the raw e-mail code.

To avoid this message corruption, please do (or ask the sender of scrambled e-mails to do) the following when sending e-mails with Apple Mail:

  1. Turn on the option Always Send Windows-Friendly Attachments (or similar) in the Attachments submenu of the Edit menu of Mail.app

  2. Make sure that the text encoding of your message is anything but plain ASCII, i.e., insert at least one non-US-ASCII character like an en-dash (Option-Dash) or a nonbreakable space (Option-Space)

Or put all attachments as the very last items of your message. [You can have Apple Mail do that automatically for you by choosing Attachments > Always Insert Attachment at End of Message from the Edit menu.] Remember that Outlook users cannot see inline attachments anyway; any attachment can only be saved and viewed with other applications.

Or send HTML-formatted (“Rich Text” in Apple jargon) e-mails. Note that the problem is created on the server, not on the client. The server is a Microsoft Exchange server, and since Microsoft’s own Exchange clients, for example Outlook, cannot display inline attachments anyway, there is apparently no need for Microsoft to hurry in resolving this issue.

See http://support.apple.com/kb/TS2928 for more information. A good discussion of the technical problem itself can be found in http://blogs.technet.com/b/exchange/archive/2011/04/21/mixed-ing-it-up-multipart-mixed-messages-and-you.aspx.