Difference between "Address Space" and "Smart Hosts" in Exchange Send Connector

I am looking at implimenting a Secure email system that is provided by PGP. The setup requires me to setup an SMTP relay from the Exchange 2007 server to the PGP server which then encrypts the email if required and sends it on.

I am making sure I understand "Send Connectors" before I mess around with them. What I need to know is what is the difference between "Address Space" and "Smart Hosts". I have looked around the internet and found that they both seem to be where the exchange server relays the emails to.However I imagine I am understanding wrong.

Please help
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tigermattConnect With a Mentor Commented:

Address Spaces define the domains to which a send connector will route mail for. For example, if a Send Connector had an address space of aol.com, then with the necessary precautions, that connector would relay email only for recipients @aol.com. Most send connectors, and the connector you'll probably want to create for the scenario you describe, would want an address space of * - indicating it will route for all domains.

It is important to note that using a * will only apply to domain names Exchange does NOT control. Exchange will always locally deliver email for your local email domains, regardless of send connector configuration. You needn't worry about 'excluding' your local domain from the send connector.

A 'smart host' is essentially an SMTP server which email sent through a send connector will be relayed off. It's equivalent to using Outlook to send email via an ISP box, which usually runs on POP3 & SMTP. The other delivery method open to Exchange - the usual one - is for Exchange to look up the recipient's mail server (MX) records and deliver the email directly.

In this instance, the PGP server would be the SMTP server email must go out via, so you would set that server as the smart host on your outbound connector.

Address Space
The address space for a Send connector specifies the recipient domains to which this connector will route e-mail, the transport type, and the address space cost. When you use the Exchange Management Console to create a new Send connector, the transport type is always configured as Simple Mail Transfer Protocol (SMTP). To configure a Send connector that uses another transport type, such as Lotus Notes, use the Exchange Management Shell to specify the transport type as part of the address space. If you use any transport type other than SMTP, you must use a smart host to route e-mail. For more information about how to configure the address space by using the Exchange Management Shell, see Set-SendConnector in the Exchange Server 2007 Help
During routing resolution, a Send connector, to which e-mail is routed for delivery to the destination domain, is selected. The Send connector whose address space most closely matches the recipient's e-mail address is selected. For example, an e-mail message addressed to Recipient@marketing.contoso.com would be routed through the connector that is configured to use the *.Contoso.com address space. When you configure a Send connector for a particular domain, e-mail that is sent to that domain is always routed through that connector. Also, the configuration settings for that connector are always applied to e-mail sent to that domain.

Using a Smart Host to Route E-mail
If you select the Internal usage type for the Send connector, you must specify a smart host. When you route mail through a smart host, the smart host handles delivery to the next hop in the delivery destination. You can use an IP address or the fully qualified domain name (FQDN) of the smart host to specify the smart host identity. The smart host identity can be the FQDN of a smart host server, a mail exchange (MX) record, or an address (A) record. If you configure an FQDN as the smart host identity, the source server for the Send connector must be able to use DNS name resolution to locate the smart host server.
The smart host for a Send connector with the Internet usage type may be a server that is hosted by your Internet service provider. The smart host for a Send Connector with the custom or internal usage types may be another e-mail server in your organization or an e-mail server in a remote domain.

Extract from
Managing Transport in Exchange Server 2007
ict-torquilclarkAuthor Commented:
Excelent. Thankyou

Makes perfect sense now!
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