RFC821 and its successors define SMTP, the transport mechanism for all Internet email. Similarly, RFC822 and its successors define the standard for Internet email content, often called MIME although MIME encoding is not mandatory - plain text will do fine.

In the years since 2001, when RFC2821 obsoleted the earlier RFC821, many people simply never got into the habit of citing RFC2821 when discussing the behaviour of MTA software. Indeed, many people seemed simply to ignore RFC2821 completely and continued to refer to the obsolete standard as a definitive guide, despite the fact that many elements of it were clarified in the later standard.

It has taken years for RFC2821 to be generally recognised as the correct standard, which is a shame because it has just been made obsolete.

The new standard is RFC5321.

Start getting used to that name now. It may actually be widely recognised before it becomes obsolete in a few years' time, though I somewhat doubt that.

RFC2822 has also been obsoleted by RFC5322.

There's a very nice write-up covering the changes here.

For me, the most interesting changes to SMTP are:

• Port 587 for message submission is now recommended. How much email is still submitted using port 25, I wonder?
  
  
• SPF and DKIM are mentioned but no sender verification scheme is yet recommended (and perhaps none ever will be).
  
  
• 550 responses after DATA are now allowed. We've been doing that for years anyway.
  
  
• IPv6 finally gets a mention.

Just ponder that last one for a moment.

If we ever do see widespread use of SMTP over IPv6, the IPv6 address space is large enough for every spam ever sent and every spam not yet sent to originate at different IP addresses.

How will DNSBLs adapt to that landscape?

Category: T'Internet
Technorati: RFC821 RFC822 RFC2821 RFC2822 RFC5321 RFC5322 IPv6

Blocked Response!07/05/2009 01:50:25

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