Recipe7.2.Choosing the Correct Connector

Recipe 7.2. Choosing the Correct Connector

Problem

You need to choose the best type of connector to create a link to another Exchange 2000/2003 routing group, Exchange 5.5 site, or foreign mail system.

Solution

The general rule of thumb for choosing connectors is simple: use a RGC unless there is a specific reason to use another connector. Luckily, these reasons are easily listed and remembered:

Use the appropriate specific connector when interfacing your Exchange organization with foreign mail systems. Exchange Server 2003 supports specific connectors for Novell GroupWise and Lotus Notes; SP1 provides support for Notes R6. In addition, the Exchange Calendar Connector allows users in your Exchange organization to bidirectionally access calendar data with these systems. Exchange 2000 also provides connectors for cc:Mail and Microsoft Mail. Other vendors may offer additional connectors.
Use the SMTP connector for gateways to the Internet, other generic foreign SMTP mail systems, or Exchange 5.5 sites that are not part of your organization. These Exchange 5.5 sites must have the Internet Mail Service configured.
Use the SMTP connector for connections between routing groups in your organization if you want to take advantage of the additional features of the SMTP connector, such as support for outbound SMTP security. This is desirable if your physical network link with the other site passes through the Internet and not over a private leased line.
In Exchange 5.5 you would use the X.400 connector for connections between sites if you need to transmit a large amount of binary traffic over a low-bandwidth link; it does not encode binary data as 7-bit ASCII like the IMS does. In Exchange 2000 and Exchange Server 2003, this is not required because the underlying SMTP transport supports the 8-bit MIME SMTP extensions.
Use the X.400 connector for connections to foreign X.400 mail systems and Exchange 5.5 sites within your organization. This connector interfaces with the Exchange 5.5 X.400 site connector.

Discussion

The advice for creating routing groups applies to connectors as well: create the absolute minimum number that you need. Most Exchange organizations will use at least one SMTP connector for passing traffic to and from the Internet (although they are not required), RGCs for connections to other routing groups, and the occasional X.400 connector for connections with Exchange 5.5 sites. These three connector types are the core connectors in Exchange 2000/2003; they can all be used to fully connect routing groups within the organization, as they will all recognize when they are talking to another routing group within the same organization and transmit all Exchange-specific traffic. These connectors have many common controls and options shown in Table 7-1.

Table 7-1. Common properties for core Exchange connectors
Property	Description
Schedules	You have the following scheduling options for the RGC and SMTP connectors: once per day, once per hour, once every two hours, once every four hours, or according to a custom schedule, which has a 15-minute resolution. The X.400 connector has a more limited set of options: always, custom schedule, or only upon remote initiation.
Local bridgeheads	You can specify one or more severs in the local routing group to act as bridgehead servers for this connector. If you do not specify any, any server in the routing group can directly send messages through this connector. You may only specify a single local bridgehead for X.400 connectors.
Remote bridgeheads	You can specify one or more servers in the remote routing group to act as bridgehead servers for this connector. If you do not specify any, messages passing through this connector will be routed directly to the appropriate destination server in the remote routing group. You may only specify a single remote bridgehead for X.400 connectors.
Direction	You can only create one-way connectors; they only handle traffic from the local routing group to the remote routing group. If you wish the connector to be bidirectional, you must establish a second connector in the remote routing group and point it back to the local routing group. If you have administrative permissions in the remote routing group, Exchange will offer to establish this second connector automatically.
Delivery restrictions	You can select Active Directory users, groups, and contacts from which to accept or reject messages. This matching is performed by email address, so it can be used to allow or deny messages from foreign mail systems; the catch is that the address must be assigned to a contact object. By default, there are no restrictions set.
Content restrictions	You can specify the properties of messages this connector will permit: high priority, normal priority, low priority, system messages, non-system messages, and message size. By default, there are no restrictions set.
Cost	Even though the RGC implements this slightly differently than the SMTP and X.400 connectors, the concept is the same: you can specify a routing cost and thus weight the different connections between routing groups to establish preferred message routes while still permitting redundancy. The RGC uses this field for the entire connector; the SMTP and X.400 connectors permit you to assign a cost to each separate address space defined by the connector.
Public folder referrals	You can specify whether referrals to public folder replicas in remote routing groups can pass over this connector.

While both RGCs and SMTP connectors use SMTP over TCP/IP, X.400 connectors can use either TCP/IP or X.25 if you have it. No matter which underlying protocol you use for X.400 connectors, you must first install the corresponding X.400 stack on the Exchange server. Because X.400 has always been 8-bit clean, X.400 connectors have traditionally been used by Exchange administrators to route large binary messages without requiring the conversion to the 7-bit ASCII (and corresponding bandwidth increase) used by the Exchange 5.5 SMTP connectors. The X.400 connector is no longer included with Exchange Server 2003 Standard Edition; this means that if you are going to be upgrading from Exchange 5.5 and require an extended period of co-existence, you will need the Enterprise Edition.