Application-generated email messages or email messages from a user in an external organization generate an NDR that has a 5.6.0 status code when messages are sent to an Exchange Server user

Consider the following scenarios.

Scenario 1

• You send an email message to a recipient.
• The email message includes an attachment.
• The mailbox for the recipient is hosted on Microsoft Exchange Server 2010 or on Microsoft Exchange Server 2007.
• The mailbox for the recipient is in an external organization.

In this scenario, the email message is not delivered to the recipient as expected. When this issue occurs, you receive a non-delivery report that contains the following status code:Scenario 2

• An application generates an email message and sends the email message to a recipient.
• The email message includes an attachment.
• The mailbox for the recipient is hosted on Microsoft Exchange Server 2010 or on Microsoft Exchange Server 2007.

In this scenario, the email message is not delivered to the recipient as expected. When this issue occurs, a non-delivery report is generated that contains the following status code:

This issue can occur if the attachment is encoded by using Base64 encoding.

Note Exchange Server accepts the standard mac-binhex encoding types.

To resolve this issue, encode the attachment by using a standard mac-binhex type as defined in RFC 1741. For example, encode the attachment by using mac-binhex40 encoding.

When the issue that is described in the "Symptoms" section occurs, the email message header contains the following Content-Type header value:When you encode an attachment by using the mac-binhex40 encoding type, the message header resembles the following:

For more information about the mac-binhex40 encoding type and about RFC 1741, visit the following MSDN website: