How Domino® modifies mail files to support IMAP

IMAP clients use a standard Domino® mail file that must be specially enabled for IMAP. If you enable IMAP access for the mail file of a registered Notes® user, the user can access the file from either the Notes® client or from an IMAP client.

A standard Domino® mail file stores information about the messages it contains within database items of the message. Notes® clients can read and interpret the information stored in these items, but IMAP clients cannot. To support IMAP clients and store IMAP-specific information, the Domino® mail file requires the addition of special IMAP database items.

IMAP stores message information within its own set of attributes. For a Domino® mail file to be used with IMAP, Notes/Domino items in the mail file have to be translated into IMAP attributes. In addition, the mail file must be set up so that all future messages delivered to it store attribute information in IMAP format.

To enable IMAP clients to access Domino® mail files, run the mail conversion utility. The conversion process places information about each message, such as its message ID and folder location, into the message's IMAP attributes, and sets a flag in the mail file that notifies the Router to add these IMAP attributes when delivering future messages.

You can run the conversion utility manually to convert mail files before users log in to the IMAP service, or set up the IMAP service so that it converts mail files automatically the first time a user logs in.

Note: To avoid possible conversion delays, run the conversion utility before users log in. Before running the conversion utility, you may first need to prepare the mail file.

Additional IMAP attributes for improving client download of message headers

When an IMAP client opens an IMAP-enabled mail file, it issues a FETCH command to the server, requesting information that enables it to display message headers. To improve performance for IMAP clients downloading message headers, the Router adds these IMAP attributes to messages delivered to an IMAP-enabled mail file:

  • $Content_Type
  • IMAP_BodyStruct
  • IMAP_RFC822Size
Note: The Router adds these attributes only if the recipient's Person document specifies MIME as the preferred mail storage format. The attributes are not added to messages delivered in MIME format to a user whose storage preference is set to Keep in sender's format.

These attributes contain summary information about the MIME content type, structure, and size of a message. Exactly how the attributes are used depends on the client. Almost all clients request size information. In addition, some request type and body structure information. If these summary attributes are present, when the IMAP service returns message headers in response to a client FETCH request, it uses the attribute information to fulfill the request, rather than opening each message to obtain the information. As a result, the client displays message headers much more quickly than it can in the absence of the summary attributes. The improved response time is especially significant for large mail files with a high percentage of messages in Notes® rich text format.

Note: The Domino® IMAP service does not use the settings on the Basics tab of the Configuration Settings document for specifying whether to return the exact size of messages. This field appears in the Configuration Settings document to provide backward compatibility with earlier versions of Domino®.

After you run the conversion utility to enable a mail file for IMAP use, you have to run the conversion utility a second time, using the -h option, to add these attributes to messages. The initial mail file conversion performed to enable a mail file for IMAP use does not add IMAP-specific attributes to pre-existing messages in the mail file, regardless of whether you run CONVERT manually or let the IMAP service automatically enable mail files. Thus messages added to a mail file before it is enabled for IMAP never contain these summary attributes.

After you enable a mail file for IMAP use, the Router automatically adds these IMAP attributes to messages, if the mail storage preference is set to Prefers MIME in the user's Person document. However it does not add them to messages stored in Notes® rich text format.