CHAPTER 3 |
SIMS Topology |
This chapter shows the SunTM Internet Mail ServerTM enterprise and services provider messaging configurations.
Topics covered in this chapter include:
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Enterprise messaging topology |
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Enterprise messaging topology with workgroup domains |
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Service provider messaging topology |
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SIMS as a Proxy mail access server |
This section shows two ways that SIMS can be configured for Bridge's internal email system at bridge.com. Notice that this view is different from the view of the email system offered to Bridge's SP customers at bridge.net.
FIGURE 3-1 shows a configuration with two SIMS systems set up at Bridge Corporation that are located behind a single firewall. This configuration supports two geographically separated offices.
In this configuration, incoming mail comes to one of the SIMS servers where it is stored in a user's. Outgoing mail goes to the server which, in turn, will either send it to a local mailbox, to one of the other SIMS servers in the intranet, or relay the message out to the Internet.
FIGURE 3-2 depicts a more complex environment with three work groups at the New York campus of Bridge.
FIGURE 3-2 SIMS Enterprise Messaging Topology with Workgroups Domains
In this topology, each of the three separate groups within Bridge has its own domain that is being hosted by a local mail server. The engineering domain and the marketing domain run SIMS, while the finance domain runs Microsoft Exchange. The main New York server also runs SIMS and is responsible for routing incoming mail to the appropriate workgroup server. Each of the workgroup servers stores messages and makes them available to the local mail clients. Outgoing mail is sent from the client to the local domain server to the New York campus server. The campus server relays the message to the appropriate Internet server outside the firewall or to the Intranet server inside the firewall.
The Tokyo campus server uses SIMS to support the email system in Japan.
Services providers have somewhat different needs and requirements than enterprises. Generally they serve a much larger customer base, they are more oriented toward POP than IMAP, and they prefer downloading email user messages to their customer's machines rather than store them in-house.
The SIMS environment in FIGURE 3-3 provides email services for Bridge's customers. It uses multiple SIMS systems that are configured to perform different responsibilities.
This system depicts a large SP using eight copies of SIMS configured to handle different responsibilities. The houses represent the SP's customers. The two large shaded boxes at the bottom represent two large message stores. Two hosts for each message store exist since the SP has installed the SIMS High Availability option. If one of the message store hosts fails, for example SIMS Host 1A, the system will fail over to the backup SIMS Host 1B.
When a customer wants to retrieve their mail, the POP request (most SPs support POP although SIMS can support IMAP if so configured) goes through the SIMS Proxy server which first authenticates the user and then forwards the request to Host1 or Host2, depending on the location of the customer's mailbox. Mail is then downloaded to the customer's machine. See "SIMS as a Proxy Mail Access Server" on page 16.
A message being sent by a customer goes through the SIMS SMTP server. The SMTP server determines whether the message destination is local or over the Internet. If the message is local, however, it sends the message via SMTP to the IMTA at either SIMS Host1 or SIMS Host2. The IMTA then sends the message to the local message delivery tool, ims_master. If the message is not local, the message is sent to the SIMS Internet Relay machine where it is forwarded to the Internet.
Mail coming from the Internet is received by the SIMS Internet Relay. If the message is local, it is sent to the message store at SIMS Host 1 or 2. If not local, the message is relayed to the next stop in the Internet.
Note that in this configuration the SIMS Proxy server, SIMS SMTP server, and the SIMS Internet Relay do not support a message store of any type.
In this deployment, a separate machine is set up to run as the LDAP master. Master directory information is maintained here, and changes to the master are filtered down to each of the SIMS hosts which acts as an LDAP slave. The auxiliary services also act as the primary DNS server.
See Chapter 5, "SIMS Architecture," for overviews of components, features, and system view of SIMS.
See Chapter 4, "Deployment Scenarios," for descriptions of several detailed scenarios, representing different models with which SIMS could be outsourced.
A SIMS proxy mail message access server (or simply proxy) operates like a regular SIMS server, but does not support a local message store. Instead, it receives POP/IMAP mailbox access requests, and then forwards these requests to the SIMS system containing the requested mailbox. FIGURE 3-4 depicts a proxy setup that shows the POP/IMAP mail retrieval path.
Proxies enable horizontal scalability (the ability to transparently expand the capacity of a SIMS environment by adding more SIMS servers) and Internet access to private Intranet mail systems. See Appendix A, "Configuring SIMS as a Proxy Message Access Server" in the Sun Internet Mail Server 4.0 Administrator's Guide for detailed information on configuring proxies.