7. 与 SMTP 扩展的交互 (Interaction with SMTP Extensions)

下表列出当前 standards-track 和 Experimental SMTP extension. 表中列出 EHLO keyword, name, 该 extension 在 submit port 上的使用指示, 以及 reference:

Keyword        Name                        Submission  Reference
----------     --------------------------  ----------  ----------------
PIPELINING     Pipelining                    SHOULD    [PIPELINING]
ENHANCEDSTATUSCODES  Enhanced Status Codes   SHOULD    [CODES-EXTENSION]
ETRN           Extended Turn                 MUST NOT  [ETRN]
 ...           Extended Codes                SHOULD    [SMTP-CODES]
DSN            Delivery Status Notification  SHOULD    [DSN]
SIZE           Message size                  MAY       [SIZE]
 ...           521 reply code                MUST NOT  [521REPLY]
CHECKPOINT     Checkpoint/Restart            MAY       [CHECKPOINT]
BINARYMIME     Binary MIME                   MAY       [CHUNKING]
CHUNKING       Chunking                      MAY       [CHUNKING]
8BITMIME       Use 8-bit data                SHOULD    [8BITMIME]
AUTH           Authentication                MUST      [SMTP-AUTH]
STARTTLS       Start TLS                     MAY       [Start-TLS]
NO-SOLICITING  Notification of no soliciting MAY       [Msg-Track]
MTRK           Message Tracking              MAY       [Msg-Track]

未来的 SMTP extension 应该 明确指定它们在 Submission port 上是否有效.

某些 SMTP extension 对 message submission 尤其有用:

Extended Status Codes [SMTP-CODES] 应该 得到支持, 并按 [CODES-EXTENSION] 使用. 这允许 MSA 比本备忘录列出的 response code 更详细地通知 client 具体配置或其他问题. 由于某些 rejection 与站点 security policy 有关, 应谨慎避免向 unauthenticated sender 暴露超过必要程度的细节.

MSA 应该 支持 [PIPELINING].

[SMTP-AUTH] 允许 MSA 验证 authority 并确定 submitting user 的 identity, 且 MSA 必须 支持它.

本备忘录中对 DATA command 的任何引用也指 DATA 的任何替代项, 例如与 [CHUNKING] 一起使用的 BDAT command.