Last week I found a message on the Technet forum which contained a question about how to disable 8 bit mime in Exchange 2007. So I started some research on mime types.

How will the mime-type be determined for example, it’s not really difficult:

  • mail without an attachment or with a plain-text attachment, this will be delivered as a 7 bit Mime this because most text is 7 bit mime based.
  • mail with jpg attachment, this will delivered as a 8 bit mime standard, when the attachment will be detected the server will convert the body to the binary type which is 8 bits.

You may discover that not all servers will support 8 bit you may get the following error when you try to connect to this server and send an e-mail:

554 5.6.1 Body type not supported by Remote Host

But how can we solve this issue:

  • upgrade to Exchange 2007 SP1, this contains a fix which should prevent this issue
  • create a speciale send-connector which uses HELO instead of EHLO

Besides this two options there exists a knowledge base article from Microsoft which tells you how you can change the smtp settings so each mail will be delivered to a 7 bit mime before it is send.



Johan Veldhuis