Migrating to Microsoft Exchange Server

"Keep a copy of all my inbound and outbound Simple Mail TransferProtocol (SMTP) mail so that I can comply with industry regulations," the customer requested.

"No problem," I said. "That feature is built into theExchange Internet Mail Connector."

"But remember," the customer said. "I don't want you to keep copies of any internal SMTP messages that travel between Exchange and my legacy mail system."

BZZZZZZZZZZ! Thanks to my alarm clock, I escaped a dream that replayed theprevious day's meeting with a new customer. The customer asked us to assist in acompany migration from Novell's GroupWise to Microsoft Exchange Server 4.0.Together we identified three key objectives:

After considering third-party gateway products, we opted for anExchange-only solution that met the customer's requirements and reducedadministrative effort. This article describes the solution and explores itsapplication in other environments.

The Solution
Figure 1, illustrates our initial plan to introduce Exchange intothe customer's messaging environment. To meet the first objective, to migrategradually and have the two mail systems coexist, we changed the function of theclient's GroupWise SMTP gateway. Previously, the gateway handled Internet-onlymessages, but we restricted it to passing all outgoing SMTP messages toExchange. This change and configuration of the Exchange Internet Mail Connector(IMC) let the two systems communicate without additional gateways.

The second objective, uninterrupted mail flow and maintaining Internet mailaddresses, required more consideration. Although we planned to use the ExchangeIMC as the conduit to the Internet, recipient addressing was a problem. Becausewe needed to address GroupWise and Exchange users at the same email domain (ourfirm.com)regardless of platform, we had to intelligently route messagesaddressed to [email protected] to either Exchange or GroupWise, depending on therecipient's migration status. Exchange's Alternate Recipient and CustomRecipient features, which let us redirect incoming messages to user mailboxes onforeign systems, solved the addressing problem and minimized overalladministration during the migration.

To achieve the third objective, archiving external communications, we hadtwo options: Develop an application to scan mail headers to distinguish andarchive external messages, or create an infrastructure extension to provideservice for external messages only. The second option proved cost-effective andeasy to support. We added a second Exchange server and IMC to the site androuted all Internet mail through it to fulfill the archiving requirement.

SMTP Configuration and Proposed Mail Routing
Our customer's existing SMTP gateway had provided a messaging link to theInternet for several months. To fulfill the first two necessities, whichrequired connecting the two mail systems, we leveraged the existing gateway as adedicated path to Exchange. We determined that with the IMC Sample ExtensionDLL, Exchange can act as a smart mail host, rerouting messages to other SMTPhosts. This solution was the key to GroupWise Internet connectivity.

Next, we created Exchange mailboxes for current email users. We alsorepresented each GroupWise user with an alias (Custom Recipient) in the Exchangedirectory and hid the aliases from view. Then, we modified delivery propertiesof each Exchange mailbox to reroute messages to an Alternate Recipient, theGroupWise mailbox alias. Table 1 lists Exchange objects and their propertiesrelevant to our plan. This configuration let us route messages from unattendedExchange mailboxes to corresponding GroupWise mailboxes and eliminatedaddressing confusion for Exchange users.

To illustrate our proposal, let's briefly follow the route for three typesof messages and their replies. First, Internet messages addressed to Exchangeusers at the ourfirm.com domain are delivered to the Exchange server. (Note: Tomake this approach work, we had to contact the customer's Internet ServiceProvider--ISP--and request modification of the MX record for the ourfirm.comdomain. We had the ISP replace the GroupWise SMTP gateway name and addressinformation with that of the Exchange server.) Likewise, Exchange performs aDomain Name System (DNS) lookup to transfer any reply or other outgoing messageto Internet mail hosts.

With the second type of message, GroupWise messages to Exchange resembleincoming Internet mail, addressed to [email protected]. (Note: The GroupWisedirectory is populated with aliases, such as [email protected], for each formerGroupWise user, to simplify addressing for GroupWise users.) By configuring theGroupWise SMTP gateway to forward all messages to Exchange, messages now arrivein an Exchange recipient's mailbox from a sender in the ourfirm.com domain.Replies and other Exchange to GroupWise messages are delivered to the GroupWiseSMTP gateway (gw.ourfirm.com) because of the address space and messagedelivery configuration.

Finally, GroupWise communication with the Internet showcases the utility ofour design. Incoming Internet mail addressed to [email protected] reaches anExchange mailbox, and the Alternate Recipient feature reroutes the mail to theappropriate GroupWise mailbox. Replies and other GroupWise mail to Internetusers pass through the GroupWise SMTP gateway and are delivered to Exchange.With the IMC Sample Extension DLL in place, if the message does not match thedomain criteria ourfirm.com, it is then forwarded (via DNS lookup) to theappropriate Internet mail host.

Archiving External Messages
In our new, somewhat elaborate, SMTP environment, the archiving objectivebecomes simpler. We already proved that with built-in Exchange features, we candistinguish and, more important, reroute SMTP messages based on domain names.Also, we know that message archiving is an optional IMC function. We concludedthat an additional IMC, dedicated to processing external messages, was our onlyrequirement.

Figure 2 shows that we added an Exchange server, Extmail, and outlinesconfiguration settings for the Our Firm site: We have two Exchange servers.Intmail is home server to all Exchange mailboxes and Custom Recipients. TheIntmail IMC routes gw.ourfirm.com messages to the GroupWise SMTP gateway and allother mail to Extmail. The message archival feature of Intmail's IMC isdisabled. We added Extmail to the site to send and receive Internet mail.Extmail uses DNS to deliver messages to appropriate Internet mail hosts. Weconfigured Extmail to archive SMTP messages.

Again, let's trace the route of messages and their replies, to examine thedesign. Assume we've already contacted our client's ISP to add an A record (DNSterminology for the record that contains the IP address and fully qualifieddomain name of a computer and that is used for name resolution) for Extmail andto modify our MX record directing mail to Extmail.

Mail from an Exchange user, [email protected], addressed to [email protected] the Exchange site via Extmail's IMC, which is configuredwith a global wildcard address space (*). Extmail uses DNS to find theappropriate mail host for whitehouse.gov and transfers the message. Extmailreceives the reply, addressed to [email protected], and subjects themessage to the criteria of imcroute.cfg (the IMC Sample Extension DLLconfiguration file). If Extmail finds a match, the message is rerouted to thelocal host and IMC handles it. After archiving the message, Extmail's IMCdelivers the message to the recipient's Exchange mailbox. No alternate recipientis specified, so the users receive the message in their inbox.

A GroupWise message to Exchange is different from our previous model. Themessage, from [email protected] to [email protected], reaches the GroupWise SMTPgateway, which directs the message to Intmail. If the message matches thecriteria in imcroute.cfg, the message path is localhost, Intmail's IMC, and themessage will be delivered to Exchange (this path includes no message archival).The reply is addressed to [email protected], which is a valid Exchange mailbox,configured to reroute mail to [email protected]. Intmail's IMC, configuredwith address space and message delivery options, transfers this reply togw.ourfirm.com. The GroupWise SMTP gateway performs a directory lookup for davejand passes the message to the user's mailbox.

Again, GroupWise messaging with the Internet is the best illustration ofour proposal. A message from [email protected] to [email protected] through the GroupWise SMTP gateway to Intmail, doesn't match domaincriteria in imcroute.cfg, enters Intmail's IMC (isn't archived), is forwarded toExtmail, doesn't match domain criteria in imcroute.cfg, enters Extmail's IMC,and is archived and forwarded to the appropriate mail host for whitehouse.gov.The reply to this message (to [email protected]) follows an equally ambitiousroute. From the whitehouse.gov SMTP host to Extmail (found via DNS lookup), themessage matches the criteria of imcroute.cfg, is rerouted to localhost, isarchived, and is delivered to Exchange by the IMC. Based on the alternaterecipient configuration (to [email protected]) of my Exchange mailbox, themessage then travels to Intmail's IMC, to the GroupWise SMTP gateway, and to myGroupWise mailbox.

Complex but Effective
Although our messaging project was not simple, Exchange Server answered ourtoughest challenges. We used NT's NetWare migration tool to create accounts andExchange's Directory Import feature and Microsoft Access to create mailboxes andCustom Recipients. Within minutes after import file setup and sample runs, wehad a complete directory of all user mailboxes, hidden Custom Recipients, andcorresponding Windows NT accounts. Later, still using Directory Import andAccess, we effortlessly modified each mailbox to include items such asdepartment and distribution list membership.

Although industry regulations for message archival are not commonplace, oursolution can be practical in countless other scenarios. For example, althoughour solution discusses migration from Novell's GroupWise, you can apply thissolution in migrations to Exchange from any mail platform that supports SMTP.Also, to comply with the Federal Records Act, many government agencies retaincopies of electronic communications involving matters of public record. Theseorganizations can use parts of our solution to archive internal and externalmail. In today's world of business partner connectivity and increased onlinevendor and customer correspondence, Microsoft Exchange has many options tooffer. Its flexibility, however, underscores the value of critical thinkingbefore implementation.