SYMPTOMS

When forwarding or smart hosting to a server the remote server rejects the message with the error "554 Body type not supported by Remote Host".

CAUSE

By default, the IIS SMTP service advertises 8BITMIME and allows MIME messages to be relayed. However, MailEnable and Microsoft Exchange Server versions 4.0, 5.0, and 5.5 are not able to handle 8-bit MIME messages.

MailEnable, like most mail servers, does not advertise the 8bit MIME extension.  This is why the IIS SMTP service cannot send to it. While MailEnable can accept 8bit MIME, it will not convert to 7bit or bounce emails if it is relaying the email as per the RFC requirements (which is why the extension is not advertised).

This is a common issue with the IIS service and relates to interoperability.

RESOLUTION

The resolution is to stop the Microsoft Windows 2000/2003 SMTP service from advertising 8BITMIME. Please review this article for further information.