Mapping MIME types to file extensions

MIME types and subtypes specify the type of program required to create or open files of that type. For example, a File identification document for JPEG files classifies files with the extension jpg as having the MIME type image and MIME subtype jpg. Domino servers and Notes® clients use the information in the File Identification documents to map file types to file extensions, and extensions to file types, on inbound and outbound mail.

This ensures that the contents of attached files are correctly interpreted by the recipient's mail client. Upon opening the message in a MIME-aware mail program, the recipient can open the attached document from within the message, provided that the mail program recognizes the MIME type and the associated application is installed on the recipient's computer.

You can create a File Identification document from the Domino Administrator by clicking the Configuration tab, expanding the Messaging view, clicking File Identifications, and then clicking Add File Identification.

You can add, modify, or delete File Identification documents from the File Identifications view of the Domino Directory. Add new documents to support additional file types. When adding a new File Identification document, you must know the MIME type for the application and the file extension associated with the application.

Modify a File Identification document in the event that a default mapping is incorrect or later standards dictate a change. You might also edit a File Identification document to specify which of multiple MIME types and subtypes Notes and Domino assign to files with a given file extension when sending outbound mail.

How Domino uses File Identification documents when processing inbound mail

When receiving an inbound MIME message that includes a file attachment, Domino reads the MIME headers to determine the name and type of the attached file. If, however, the MIME headers do not specify the name of the attached file, Domino must assign a name to the file that is both unique within the document and includes the appropriate file extension. To determine the file extension to use in creating the file name, Domino refers to the File Identification documents in the Domino Directory.

For example, if Domino receives a message that has a MIME header indicating that it contains a Microsoft™ Word attachment (MIME type/subtype of application/ms-word), but neither the content-type header or content-disposition header specify a file name, the server has to provide a name for the attachment. To ensure that Domino creates a name using the correct file extension for a file of this type, the server checks the Domino Directory for a File Identification document for this file type and subtype, and then checks the Extension field of the matching document. Because, by default, the only document that matches files with the MIME type application/ms-word indicates that the file uses the extension DOC, Domino creates a file name using this extension.

By default, the File Identifications view of the Domino Directory lists multiple documents for a given MIME type/subtype alphabetically, by file extension. For example, by default, Domino includes several File Identification documents for the MIME type/subtype application/vnd.lotus-1-2-3, and the default view lists these in ascending alphabetical order, beginning with the document that specifies the extension 123 and proceeding through those that specify the extensions unknown, WK2, WK3, WK4, and WKS. This list order determines how Domino names files when receiving a message containing an unnamed file attachment with one of these MIME types. When creating the file name, the server uses the information in the first document that appears alphabetically in the view.

How Domino uses File Identification documents when processing outbound mail

Domino servers and Notes clients both use File Identification documents when sending MIME messages that include file attachments. In both cases, information in the document is used to specify the MIME content type of the message attachment.

Domino servers use File Identification documents when converting messages that include file attachments from Notes rich-text format to MIME format for sending over SMTP. When converting an outbound message that includes a file attachment, Domino first searches for a File Identification document that corresponds to the file extension of the attachment. After locating the correct document, Domino uses the MIME type and subtype information from the document to construct the MIME Content-type header for the message part that describes the attachment.

When a Notes client attaches a file to a message it sends in MIME format (for example, when sending to Internet recipients or to Notes mail recipients whose mail storage preference is set to MIME), the client first checks the operating system to determine what file associations are defined. Clients running on Microsoft Windows™ check the Windows registry, while clients running on the Macintosh check Internet Config. If the client cannot locate MIME type information from these sources, it then checks the Domino Directory for a File Identification document that applies to files with the same extension as the attached file. After locating the correct document, the client places the MIME type and subtype information from the document in the MIME header describing the attachment.

In the case of both servers and client, if more than one File Identification document applies to a given file extension, the setting in the Outbound field of the documents determines which MIME type and subtype to assign to file attachments with this extension when sending mail.

To create or modify a File Identification document

1. From the Domino Administrator, click the Configuration tab and expand the Messaging view.
2. Click File Identifications.
3. To add a new File Identification document, click Add File Identification.

   To edit an existing File Identification document, select it from the documents listed, and click Edit File Identification.

4. Complete the following fields:

   Table 1. File Identification document fields

   Field	Description
   MIME type	General MIME category used to describe files of this content type or media; for example, application, audio, image, or video. When sending attachments in MIME messages, the information in this field is placed in the MIME Content-type header. Each MIME type/subtype combination can be mapped to zero or more file extensions.
   MIME subtype	The specific MIME category that uniquely identifies the application that created files of this content type, for example, X-Lotus-NSF. When sending attachments in MIME messages, the information in this field is placed in the MIME Content-type header. Each MIME type/subtype combination can be mapped to zero or more file extensions.
   File extension	The Microsoft Windows or UNIX™ file name extension associated with files of this type; for example, JPG, BMP, or NSF. The Domino Directory can contain multiple File identification documents for a given file extension. If the MIME headers of an inbound message do not specify the name of an attached file, Domino creates a file name for the attachment using this extension.
   Description	The type of file or the name of the application used to create and open the file.
   Outbound	If the Domino Directory contains multiple File Identification documents for files with this file extension, this setting determines which MIME type and subtype Notes and Domino use to send file attachments with this extension. Note: Notes clients also use settings in the Microsoft Windows registry or the Macintosh Internet Config object to determine the MIME type and subtype to associate with a given file extension. Choose one: Send - When sending outbound messages in MIME format, Domino assigns this MIME type and subtype specified in this document to attachments that have this file extension. If there are multiple File Identification documents for a given file extension, select this option for one document only. If the value in this field is set to Send in multiple File Identification documents for a given file extension, Domino uses the first document listed in the File Identifications view to set the MIME information for attachments with the extension. Do not send - When sending outbound messages to MIME format, Domino does not assign the MIME type and subtype specified in this document to attachments that have this file extension. If there are multiple documents for a given file extension, specify this option in the Outbound field in all but one of the documents.