最後更新: 2023-12-27

目錄

• EHLO Keywords
• smtpd_discard_ehlo_keywords
• DSN
• CHUNKING

EHLO Keywords

SIZE - Message size declaration, RFC 1870

PIPELINING - Command pipelining, RFC 2920

DSN - Delivery status notification, RFC 3461

ETRN - Extended version of remote message queue starting command TURN, RFC 1985

PIPELINING - Command pipelining, RFC 2920

smtpd_discard_ehlo_keywords

smtpd_discard_ehlo_keywords (default: empty)

A case insensitive list of EHLO keywords (pipelining, starttls, auth, etc.)
 that the Postfix SMTP server will not send in the EHLO response to a remote SMTP client.

i.e.

/etc/postfix/main.cf

smtpd_discard_ehlo_keywords = silent-discard, chunking, size

 * silent-discard: to prevent this action from being logged

DSN

DSN needs modification on the protocol level MAIL FROM or RCPT TO command

-->  MAIL FROM: [email protected] RET=HDRS
<--  250 2.1.0 Ok
-->  RCPT TO: [email protected] NOTIFY=FAILURE,DELAY ORCPT=rfc822;[email protected]
<--  250 2.1.5 Ok

CHUNKING

Postfix: It is enabled by default.

C: MAIL FROM:<[email protected]>
S: 250 2.1.0 Ok
C: RCPT TO:<[email protected]>
S: 250 2.1.5 Ok
C: BDAT 10000
C: ..followed by 10000 bytes...
S: 250 2.0.0 Ok: 10000 bytes
C: BDAT 123
C: ..followed by 123 bytes...
S: 250 2.0.0 Ok: 123 bytes
C: BDAT 0 LAST
S: 250 2.0.0 Ok: 10123 bytes queued as 41yYhh41qmznjbD
C: QUIT
S: 221 2.0.0 Bye

ETRN

Extended Turn

To request the remote server to send any pending email messages that are queued for a specific domain.

用圖: 當 Mail Server online 後可以叫 backup(MX) server 傳返 downtime 時收到的信過來.(queued messages)