Electronic Mail Service System

  The electronic mail service system is the subsystem that responds to the requests for service generated by the service agents discussed in . An overview of the electronic mail service system appears in figure .

techsystemTechnical Infrastructure

The components of the electronic mail service subsystem currently identified include:

Postoffice Service System

The postoffice, or Mail Store (MS) in the X.400 model, provides a per-client repository for pending mail that the client has received but not yet read, termed a ``mailbox''. The postoffice is responsible for actually managing the client mailbox, as directed by the MUA. The functions implemented by the postoffice may include:

• per user authentication of mailbox ownership
• authenticated read/write/modify access to a mailbox for the mailbox owner
• access control to allow designated client's access to a mailbox other than their own.
• encryption of traffic between the MS and the MUA
• per message privacy control, to prevent authorized non-owners from reading individual messages

It is intended that the client should keep archival and reference mail stored on the local platform. The implementation may provide a limited amount of space on either a client or group basis for storage of read, but unfiled, mail. The storage control system should:

• provide resource controls on a per-client or per-group basis, such that available storage cannot be consumed by a single user
• provide direct user notification when the user comes within a threshold of the resource bound
• make every effort to not lose or reject inbound mail due to the storage control system
• provide a secondary storage medium on which to store client messages that have aged according to published time interval. Obviously some retrieval mechanism is necessary as well. This system could be activated directly by a client command, to handle vacations and other long absences.
• preferentially move read, but unfiled mail to a secondary storage medium, such as tape or hard copy.

Mail Transport System

The mail transport system provides the relay function of the electronic mail service. It accepts a electronic mail message, composed of a body, a correctly addressed header and it forms an ``envelope'' that contains the next hop information provided by the mail routing system. The transport system delivers the message via the next hop identified in the envelope to the intended client within the institutional electronic mail system or to an external gateway, for delivery externally.

The MUA may use the transport system directly to submit mail for transmission, or it may use a specialized protocol for that task.

A delivery receipt may be returned to the sending client MUA if so requested after successful delivery. Misaddressed mail is returned to the originating sender, if possible.

Mail Routing System

Once a mail message has been submitted for transmission, the the address identifying the mail store is examined in order to resolve the path to forward the message along. The mail routing system is then responsible for providing the translation from an electronic mail address to routing information that the transport system can utilize in forwarding the electronic mail message through the network. This usually involves providing a subsystem that facilitates the translation of electronic mail addresses to next hop addresses.

Directory Service System

The directory service system accepts well-formed requests, via a Directory Access Protocol (DAP), for the purpose of discovering the electronic mail address given a (possibly incomplete) specification of another electronic mail user's name, department, organization or other such information. If the query is for a local client, it interrogates an institutional directory and attempts to return a response that reflects the electronic mail address of that client. If the the query is for a electronic mail user at another organization, an appropriate external protocol such as X.500 is used to further the query. It may be that there are multiple external protocols in use. The external gateway for the directory service system may use more than one.

Administration Service System

The administrative system is responsible for managing the information required by all components of the electronic mail system, at the direction of authorized administratives service agents. Information managed by the administration system may include:

• client information
• authentication information
• associations of clients to mailboxes
• aggregations of clients into groups
• associations of local electronic mail administrators to groups
• group alias and address lists
• group and group member resource limits
• business forms
• group and group member administrative options
• performance metrics
• directory information

Mechanisms must exist to support large volume creation, deletion and modification of the managed information. A design objective of the administrative system must be to minimize the number of person hours required by the administrative management task. This implies the system should be paperless, and as automated as possible.

External Gateways

In this section ``external'' means that the gateway is a transfer point into another electronic mail or messaging system that is not part of the supported institutional electronic mail service. This may include other electronic mail systems within the University that are not provided or supported by UTCC.

Internet

The institutional electronic mail service must have a robust, reliable, multi-threaded Simple Mail Transfer Protocol (SMTP) gateway. The gateway must understand the Domain Name System (DNS) [Moc87a], [Moc87b].

BITNET

The institutional electronic mail service must provide a gateway to the BITNET mail system, including NETNORTH.

Envoy 100

The institutional electronic mail service should provide a gateway to the commercial ENVOY 100 electronic mail service for connectivity to major X.400 mail services.

Fax

The institutional electronic mail service should provide a gateway to convert electronic mail to fax images, and automatically send them. No human intervention should be required to handle or route messages. This restriction may prevent a bi-directional gateway. However, a unidirectional, email to fax gateway is still very desirable. This gateway can facilitate the reception of mail by non-subscribers, or those without computers.

Campus Mail

The institutional electronic mail service should provide a gateway to allow electronic mail to be printed out on paper and delivered to an intended recipient via the campus mail system. This will facilitate the reception of mail by non-subscribers, or those without computers.

Voice Mail

The institutional electronic mail service may provide a gateway to the voice mail system. This might permit voice mail notification of electronic mail, electronic mail notification of voice mail, or reception of electronic mail via the voice mail system. This gateway could be a further mechanism for non-subscribers to participate in the world of electronic mail.

Text Pagers

The institutional electronic mail service may provide a gateway to a text pager system. Text pagers are used across the campus for various purposed, and this would facilitate participation of mobile staff in the electronic mail system.