Home / server / Questions / 1046794
Accepted
71GA
Asked: 2020-12-19 10:14:26 +0800 CST

Email "submission" and "relay" event

  • 772

I want to get to the bottom of the term email "submission" and "relay". So what does this really mean?

In my head I have two possible scenarios:

SCENARIO 1

What the terms mean is:

  • "relaying" ⟹ "event of sending email using SMTP protocol"
  • "submission" ⟹ "event of recieving using SMTP protocol"

In this scenario I have to always tell who in the email chain I am refering to.

SCENARIO 2:

What the terms mean is:

  • "relaying" ⟹ "event of email passing through any device using SMTP protocol (email is recieved & sent ie. forwarded)"
  • "submission" ⟹ "event of sending using SMTP protocol"

So which scenario is correct?

smtp

1 Answers

  1. Best Answer

    Scenario 2 is close if "sending" is stated as the initial event, authenticated or authorized, of handing mail to the distribution system of email, handled by mail-transfer-agents. Submission can only happen once during the lifecycle of mail delivery - at the beginning. Any other smtp to smtp transfer between MTAs is named relaying.

    The submission split from the ongoings of port 25 is currently defined in rfc 6409. Reading its introduction explains the reason why unrestricted mail relaying needed an additional concept of "authenticated/authorized" sending, thus "submitting" of mail.

    So to reiterate a common lifecycle of an email nowadays is

    client (mail-user-agent) => submission (mail-submission-agent, part of the smtpd) => relay*(n) => delivery

    If you configure a postfix and even use a traditional mail program as mutt (check their MailConcept page), you see how it's very much a lot of small services combined at every step.

    • 1