On-Demand Mail Relay

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ODMR (On-Demand Mail Relay)
Family: Internet protocol family
Operation area: Collection of email (mail transfer)
Ports: 366 / TCP

366 / UDP

ODMR in the TCP / IP protocol stack :
application ODMR
transport TCP
Internet IP ( IPv4 , IPv6 )
Network access Ethernet Token
bus 		Token
ring 		FDDI ...
Standards: RFC 2645 ( 1999 )

On-Demand Mail Relay ( ODMR ) or Authenticated TURN ( ATRN ) is an extension for the e-mail protocol Simple Mail Transfer Protocol (SMTP) . ODMR is defined in RFC 2645 .

ODMR is an e-mail service that allows users to collect their e-mails from an Internet Service Provider (ISP) using dynamic IP addresses after appropriate authentication .

In contrast to POP3 , the e-mail to be picked up is sent including the SMTP envelope, which is important for the assignment to a recipient.

The client connects to the ODMR server and is authenticated by it. He queries all emails for his domain . The client and server then swap roles, and the e-mails are transmitted over the existing TCP connection via SMTP.

This method is interesting for users who do not have a permanent Internet connection , for example for users with an ISDN dial-up access and for users with changing IP addresses, which, for B. applies to many ADSL offers.

ODMR server

ODMR servers are already integrated in some MTAs (e.g. ALT-N MDaemon), but there are also extensions for common Unix MTAs such as Sendmail, Exim, Postfix and qmail.

ODMR client

For example, fetchmail can be used as an ODMR client . Example for a configuration in fetchmail: 

poll odmr.mailserver.de
    proto odmr:
    user "benutzername" password "password"
    fetchdomains "domainname.de"

When using under Unix it is important that /etc/servicesthe network ports are configured: 

odmr 366/tcp # odmr
odmr 366/udp # odmr

otherwise a socket error message is issued.

Commands

EHLO
The EHLO command is the same as in SMTP . The client's response must contain AUTH and ATRN.
AUTH
AUTH is defined in RFC 2554 . It uses a SASL mechanism that is defined in RFC 2222 . The session is considered unauthenticated until a successful response has been sent to AUTH. CRAM-MD5 support is mandatory for ODMR servers and clients.
ATRN
When the client sends ATRN to the server, it receives the e-mails for all authorized domains.
QUIT
This command ends the session.

Example of a typical ODMR connection: 

>  220 EXAMPLE.NET on-demand mail relay server ready
<  EHLO example.org
>  250-EXAMPLE.NET
>  250-AUTH CRAM-MD5 EXTERNAL
>  250 ATRN
<  AUTH CRAM-MD5
>  334 MTg5Ni42OTcxNzA5NTJASVNQLkNPTQo=
<  Zm9vYmFyLm5ldCBiOTEzYTYwMmM3ZWRhN2E0OTViNGU2ZTczMzRkMzg5MAo=
>  235 now authenticated as example.org
<  ATRN example.org,example.com
>  250 OK now reversing the connection
<  220 example.org ready to receive email
>  EHLO EXAMPLE.NET
<  250-example.org
<  250 SIZE
>  MAIL FROM: <Lester.Tester@dot.foo.bar>
<  250 OK
>  RCPT TO: <l.eva.msg@example.com>
<  250 OK, recipient accepted
...
>  QUIT
<  221 example.org closing connection

literature

  • RFC 2645 (ON-DEMAND MAIL RELAY (ODMR): SMTP with Dynamic IP Addresses)
  • RFC 2554 (SMTP Service Extension for Authentication)
  • RFC 2821 (Simple Mail Transfer Protocol)

See also

Web links