D
Co-existence

This section discusses how Oracle Email can co-exist with other mail systems.

This appendix contains the following topics:

• Overview
• MX Records
• Oracle Email Co-existence Features

Overview

Email systems are, by design, intended to co-exist with other systems. Industry standards, such as SMTP and MIME, enable the exchange of information between users. In some organizations, a deeper level of co-existence is required. For example, during the process of migrating from a legacy e-mail product to Oracle, both the old and new systems are operational. Some special considerations are required for the continued delivery of messages in these environments.

The following are examples of co-existence:

• You have an Oracle Email system, and you need to exchange messages with the outside world.
• You are migrating, and need to co-exist within your organization for a short period
• Other units of your organization use other mail systems, and are not migrating to Oracle Email

MX Records

The main issue co-existing environments must address is the role played by the exchanger (MX) record. The MX record value defines the physical network address of messages for a given e-mail domain. Remote message transfer agents (MTAs) can only resolve this address by domain name.

Routing messages to the correct system of the destination mailbox can be solved in the following ways:

• Each co-existing mail system maps to a unique domain name. This is the simplest method to implement, but can be less convenient for users. A single enterprise e-mail domain for all users is not possible, and a user's address is dependent on their e-mail system.
• Manage an alias database, possibly at an additional inbound MTA, that maps domain addresses to their destination inbox. This method works well, but creates some extra complexity for the mail administrators.
• Configure the mail system to intelligently route non-local messages to the other system. This method satisfies most requirements, although support for this type of behavior varies between vendors.

Oracle Email Co-existence Features

When messages arrive at the Oracle Email MTA, the address is examined to determine if the addressee is local. This is checked by matching the address against the Local Domains server setting. If the domains match and directory lookup fails to resolve the address, then the address is unknown. If the domain does not match any of the local domains, the message is kept in the relay queue.

In special circumstances, the MTA does not reject the message, but it relays it to another MTA. Server settings enable the MTA to be configured to pass on any message that is addressed to a valid local domain, but where the mailbox address is unknown. This method enables messages to be addressed using a single global domain, without the need for managing an alias database.

Perform the following steps to enable this feature:

1. Add the flag -l to the Mail Process Flags parameter of the MTA processes.
2. Set the Relay Host parameter to the name of the MTA to route messages.

Aliases and Rewriting Rules

A successful co-existence strategy requires that different systems can exchange messages with each other, and that users can easily address messages to reach the intended recipient.

Features of the Oracle Email, such as aliases and address rewriting rules, can assist in co-existence. Aliases provide a simple way for users to look up recipients in a directory, without needing to understand details of how messages are routed inside the system. Address rewriting rules to assist co-existence by recognizing addresses and automatically altering the intended routing path.

For example, in some cases it may be necessary to route messages to their target by including the actual location of the mail server, such as [e-mail] instead of [e-mail]. Such an address enables the successful transport of messages from one system to another, but may result in delivery failure since the full e-mail address is not recognized at its destination. Using address rewriting, the pattern *@smtpin.acme.com can be rewritten to *@acme.com to ensure that the recipient mailbox is found. Using aliases, users can easily select address messages from the directory without needing to know the details of the actual e-mail address required for delivery.

Troubleshooting

When configuring Oracle Email in a co-existence environment, it is sometimes difficult to trace exactly why problems occur. In order to debug any problems, you need to be familiar with the underlying protocols and routing of e-mail. Problems typically occur due to incorrect message addressing, or unexpected address re-writing by intermediate MTAs, particularly through Sendmail.

Troubleshooting tips include:

• Ensure that you fully understand the exact route that messages take between the different MTAs in your organization, and how each of these process messages in their delivery.
• ensure that messages are deliverable from this MTA, if you are routing messages to unknown mailboxes in the local domain to a relay machine.
• When routing messages to Oracle Email from another MTA, ensure that the exact address matches against the Local Domains and any appropriate re-writing rules of the SMTP Inbound processes.
• Check that messages are actually delivered to Oracle Email with the correct addresses by using debugging tools such as command-line mail (on Unix), or by using Telnet to the SMTP Inbound port directly.
• Increase the log level of the SMTP Inbound processes and examine the process log files. The log records attempted mail delivery to Oracle Email, including sender and recipient address information.