Re: T2 Retry with Delivery Receipt

[Dan Weinreb <dlw@exceloncorp.com>]

   Date: Fri, 14 Sep 2001 10:31:14 -0400
   From: Martin W Sachs <mwsachs@us.ibm.com>

   I completely agree with your conclusion but I am curious about SMTP.  When
   I send an email, I send it to the email address that I know for the
   destination.  When I receive an email, the sender sends it to my email
   address.  Yet the header information may show that this email has travelled
   through lots of intermediary mailers.  I don't know how the routing
   mechanism works but I do know that I don't have to care about it.  I am
   doing end to end addressing.  And yes, it is below the level of ebXML but
   it is an example of unreliable intermediaries.

Yes, I agree with all of this.

(If you're curious about how the email routing works, here's
the basic explanation I have:

  Basically, the client does a DNS lookup for MX records, finds
  the one of best preference (lowest number) that it can reach,
  and sends the mail there.  The server to which it delivers
  either delivers the mail to a user (or user mail store), routes
  it elsehwere based on local knowledge, or repeats the process,
  looking for a server that is more-preferred than it is.  There
  are many subtlties, but the basic system is pretty simple.

See RFC2821 for full info; RFC974 for an earlier treatment.