The core Internet transmission protocol is TCP/IP, which carries all Internet traffic. Mail traffic has its own protocol, SMTP, which supports only the rudimentary text format. Still, this standard has worked reliably for about 18 years and has been supported by virtually every major messaging system. The
figure shows
the basic model for SMTP.
SMTP gets your messages only as far as th
e client, however, and does little else. It does not, for example, guarantee delivery, issue a return receipt, allow "unsending," or carry attachments -- all common features in proprietary messaging environments. However, other Internet standards exist for these and other features.
POP and IMAP
Once a message reaches the client, two other standards come into play. Post Office Protocol (POP) and Internet Message Access Protocol (IMAP) determine how you retrieve a message. POP's latest version, POP3, is rather limited. It requires that messages be kept in a store on a server. When you want messages from this store, you have no choice but to download them all to your local system. Still, POP3 is an important link between Internet and proprietary e-mail systems because all the major vendors support it.
The latest version of IMAP, IMAP4, gives you more choices than POP3 on how to retrieve messages. With it, you can check the messages in the store before downloading them. You can then s
elect what you want, even just part of a message, and leave the rest on the server. Messages stay there until you delete them. These features are important conveniences, but they also make it easier to archive and share messages -- something proprietary systems already do well.
Most vendors and analysts expect that IMAP eventually will replace POP3 although they currently coexist on many implementations. (For example, Microsoft and Lotus currently support POP3 in all their messaging products and will have IMAP4 support in the first quarter of this year.) The significance here is that, as with a pure Internet e-mail system, proprietary servers like Microsoft Exchange or cc:Mail will support any POP3- or IMAP4-compliant client.
ACAP and IMSP
Beyond IMAP is Application Configuration Access Protocol (ACAP). ACAP enhances IMAP by letting you set up address books, user options, and other data for universal access. At this writing, no Internet or proprietary products have implemented ACA
P because the Internet Engineering Task Force (IETF), the group responsible for developing Internet standards, has not yet approved the final specification. A final spec should be out early this year, and implementations will likely follow soon after. In the meantime, some Internet products use Internet Messaging Support Protocol (IMSP), a less robust standard than ACAP. However, IMSP will probably fade away in favor of ACAP. (For more information on POP, IMAP, and ACAP, see "E-Mail Grows Up" in the December 1996 BYTE).
LDAP
For ACAP to do its job, it needs to work within a standard directory services structure. Lightweight Directory Access Protocol (LDAP) provides that structure. LDAP is a subset of the X.500 directory commonly used in many LANs. (
See the figure.
) It runs over TCP/IP and uses a simplified data representation for protocol elements. LDAP clients are, therefore, smaller, faster, and easier to implement than X.500 clients. LDAP is vendor-independent
and works with, but does not require, X.500. (See "LDAP Unites the Internet" in the December 1996 BYTE.)
Standard
Status
SMTP Widely deployed
POP3 Widely deployed
IMAP4 Soon to be widely deployed
IMSP Deployed mainly among native Internet products
ACAP IETF spec expected late 1997
MIME Widely deployed
S/MIME Spec not finalized, but some implementations exist
LDAP Widely deployed
Calendaring/ IETF spec expected mid-1997
Scheduling
Fax IETF spec expected mid-1997
EDI IETF spec expected late-1997
Voice IETF spec expected mid to late 1997
Receipt IETF spec expected
Notification mid-1997
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Internet Standards
