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Messaging Server, RBL, and dns_verify (Doc ID 1932937.1)

Last updated on OCTOBER 31, 2019

Applies to:

Oracle Communications Messaging Server - Version 5.0.0 and later
Information in this document applies to any platform.

Purpose

This article will address questions around the use of Real-time Block Lists (RBLs) and Domain Name Service (DNS) Verification in the Messaging Server MTA.

RBL and DNS Verification are actually separate things. But RBL checking makes use of dns_verify. This article is more about how to use the dns_verify routines.

Questions and Answers

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In this Document
Purpose
Questions and Answers
 Do you really want to do this?
 Realtime Block Lists (RBLs)
 Normal DNS Usage by the MTA
 Two things called DNS Verify
 DNS Verify and RBL
 Ok, How do I use this?
 Options for configurating RBL
 ENABLE_RBL or DNS_VERIFY_DOMAIN in dispatcher.cnf
 The dns_verify library routines
 A brief word about mappings tables
 Use the dns_verify_domain_port routine in the PORT_ACCESS table
 Use the dns_verify_domain routine in the MAIL_ACCESS or ORIG_MAIL_ACCESS tables
 Syntax of dns_verify_domain and dns_verify_domain_port
 Continuation Lines in Mappings Tables
 Use the dns_verify (or dns_verify_ptr) routine in any table
 The dns_verify_ptr argument syntax
 Using dns_verify to do RBL lookups
 When DNS fails - why you need return-if-indeterminate
 Symbolic Substitution - Return Values
 MTA Performance problems caused by RBL and DNS performance
 Why is it so bad?
 What else can we do about it?
 Or have local users go thru a different service
 Improvements in Messaging Server 6.3
References

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