Summary

  • RFC 821 offered three optional transaction verbs that made terminal presentation, mailbox deposit or both part of SMTP delivery semantics.
  • Their success conditions differed: SEND depended on terminal delivery, SOML accepted either destination, and SAML depended on the mailbox even when it also tried the terminal.
  • MX relaying separated knowledge of the mail route from control of the user's live screen; later SMTP therefore deprecated the verbs while preserving narrow compatibility rules.

Three verbs, three kinds of arrival

Picture a user seated at a shared host in 1982. The user is logged in and has allowed messages to appear on the terminal. A remote sender opens an SMTP session, but instead of beginning with the ordinary MAIL command, it chooses among three alternatives.

SEND asks for the message to reach the terminal. If the user is absent or refuses terminal messages, the receiving system may reject that recipient temporarily. SOML—Send Or MaiL—tries the terminal when the user is active and willing, then falls back to the mailbox. SAML—Send And MaiL—tries the terminal and deposits the message in the mailbox regardless.

These were not decorative headers. RFC 821 made each verb a transaction opener, followed by RCPT and DATA. The sender selected the delivery behavior before supplying the recipients and body.

The design looks like a primitive notification preference, but it carried a heavier promise. SMTP was not only transporting a message toward an address. It was being asked to interpret whether a person was presently reachable, whether that person accepted interruption, and whether a visible event or a stored copy counted as success.

Success changed with the verb

The fine print reveals why the three commands are historically valuable. They separated outcomes that modern interfaces often collapse into a single word: delivered.

For SEND, the transaction was successful only if the data reached a terminal. A mailbox copy was not the fallback unless the client had chosen a different verb. For SOML, terminal display and mailbox deposit were substitutes; either could satisfy the request. For SAML, the mailbox was mandatory and terminal display was additional. Its success condition was mailbox delivery, not proof that the user saw the live presentation.

One protocol therefore exposed three evidence models. A successful SEND could mean momentary presentation without durable storage. A successful SOML did not say which destination won unless the implementation supplied further evidence. A successful SAML established the mailbox branch but did not make the screen branch part of the success guarantee.

This was an unusually honest grammar. It admitted that attention and custody were different services. The difficulty was that the originator, by choosing the verb, appeared to choose consequences borne by a recipient and by infrastructure it did not control.

Presence was a local fact

Terminal delivery depended on two conditions in RFC 821: the user had to be active on the host and accepting terminal messages. Neither condition was a property of an email address. Both belonged to a session on a particular machine at a particular moment.

That distinction matters. An address can remain stable while a user logs out, switches terminals or changes an interruption preference. A mail route can remain valid while the receiving host no longer owns the user's interactive session. Even within one transaction, the state observed during recipient processing can change before the body arrives.

The receiving host therefore retained the actual decision. The client could request SEND, but it could not declare the recipient present. An advertised command could prove that the server understood the vocabulary, but not that this person was online or consenting now.

The authority boundary was already visible: the sender expressed intent; the recipient side controlled presence, consent and the destination that could be completed.

MX relaying broke the apparent shortcut

RFC 1123 made implementation of SEND, SOML and SAML optional for both senders and receivers. Its short discussion identifies the architectural fault line.

Mail Exchange routing lets a host accept mail on behalf of a destination. That host may know how to move the message closer to the user, yet be unable to write directly to the user's terminal. For a recipient following SEND, RFC 1123 allowed such a receiver to return 251 User Not Local, telling the originator that delivery could be deferred.

The reply exposed two kinds of reachability. Route reachability meant the system could take responsibility for forwarding mail. Presentation reachability meant it controlled the screen on which the user was active. An MX could possess the first without the second.

That is more than an old implementation nuisance. It shows why a distributed store-and-forward network cannot make live attention a reliable property of an intermediate hop. The relay may have excellent routing authority and no presentation authority at all.

Extension discovery could advertise grammar, not presence

When RFC 1425 introduced SMTP service extensions, its initial registry listed the three commands as optional services. Each command name also served as an EHLO keyword.

That move made support discoverable. A client no longer had to guess whether the server recognized the verb. But discovery narrowed only one uncertainty: syntax and implementation capability. It did not answer whether a recipient was logged in, whether terminal messages were enabled, whether the current server was final, or whether display would survive the trip.

The distinction is easy to lose in products. A capability flag often becomes a green button, then a promise. Here, EHLO could truthfully say “this server implements SEND” while saying nothing about the human state on which a particular SEND depended.

Compatibility survived after the design lost its centre

By 2001, RFC 2821 called SEND, SAML and SOML obsolete. It said the commands had been rarely implemented and that workstation changes and other protocols may have made them obsolete even where code remained.

The standard did not pretend that old vocabulary could simply vanish. Clients were told not to provide the commands as services. Servers were still allowed to implement them, but only with the RFC 821 model and explicit EHLO advertisement.

RFC 5321 preserves that settlement. The obsolete verbs remain recognizable transaction starters, yet ordinary SMTP is organised around MAIL and the formal transfer of responsibility that follows successful acceptance of message data.

That responsibility boundary is durable. Once a server accepts the data with success, it owns the obligation to deliver or report failure. It does not need to claim that a person's eyes met a screen at a specific instant.

Deprecation therefore reduced authority without breaking every old implementation. The Internet kept a narrow compatibility path while moving its interoperable centre toward a claim the transport could actually sustain: custody of a message, not custody of attention.

The registry is a record, not a deployment report

The IANA SMTP registries still list SEND, SOML and SAML. The entries retain their RFC 821 meanings, note later deprecation and mark them MUST NOT for Message Submission use.

Their presence is historical and operational vocabulary. It does not show how many servers implement the commands, whether any recipient accepts terminal messages, or whether a specific display occurred. Registration coordinates names; it does not revive the social assumptions behind them.

This is the evidence boundary that makes the story useful today. Support, presence, consent, presentation, storage and responsibility are six different facts. Early SMTP put several into one transaction choice. Later SMTP did not solve human attention; it stopped making that transient state the centre of mail transport.

What the abandoned branch teaches

The three commands were not foolish. On a small set of closely coupled hosts, direct terminal delivery could be convenient and intelligible. SOML offered graceful fallback. SAML explicitly preserved a durable copy. The designers saw real distinctions and gave each one a verb.

Scale changed which distinctions belonged on the wire. As relays, heterogeneous workstations and separate user applications multiplied, the transport could reliably own queueing and custody. It could not reliably own the user's current surface or willingness to be interrupted.

The lost commands leave a precise lesson: real-time display is not a stronger form of delivery. It is a different event, controlled by a different principal and supported by different evidence. A glowing screen can be immediate and ephemeral. A quiet mailbox can be delayed and durable.

The message that arrived before the mailbox may have won the race. It had not necessarily found a place to stay.

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