Topic Last Modified: 2007-05-16

Use the Advanced Delivery dialog box to set routing options on your SMTP virtual server. The following options are available on the Advanced Delivery dialog box:

Maximum hop count

When a message is delivered, it may be routed to several servers before it reaches its final destination. You can designate how many servers that the message can pass through. This is known as the hop count.

After the hop count is set, the SMTP virtual server counts hops that are listed in the Received header lines of the message header. When the number of Received fields exceeds the maximum hop count setting, the message is returned to the sender with a non-delivery report (NDR). By default, the maximum hop count value is 15.

Masquerade domain

The masquerade domain name replaces the local domain name listing in Mail From lines in the SMTP protocol.

Fully qualified domain name

Two records can be used to identify and verify a computer in a TCP/IP network:

  • The mail exchanger (MX) record

  • The address (A) record

The MX record identifies the host and domain name associated with the SMTP virtual server. The MX record uses the fully qualified domain name (FQDN) for the domain name. The A record identifies the IP address for the computer. When both records are used, name resolution occurs faster.

For Windows Server 2008 SMTP Server to process MX records, an FQDN must be designated. An FQDN is used by Domain Name System (DNS) to identify the host server for a domain. The syntax is host.domain. For example, may have several host servers, with one named Server01. The FQDN for the server would be

By default, the FQDN is the name of the default domain configured for the SMTP virtual server. To override the automatic use of the default domain, change the FQDN on the Delivery tab.

Smart host

You can route all outgoing messages for remote domains through a smart host instead of sending them directly to the domain. This lets you route messages over a connection that may be more direct or less costly than other routes. The smart host is similar to the route domain option for remote domains. The difference is that after a smart host is designated, all outgoing messages are routed to that server. With a route domain, only messages for the remote domain are routed to a specific server.

Make sure that the designated smart host is optimized for security and administered by a trusted authority, especially when forwarding sensitive information.

If you set up a smart host, you can still designate a different route for a remote domain. The route domain setting overrides the smart host setting.

Type an FQDN or an IP address to identify the smart host. If you use an IP address, enclose it in brackets [ ] to enhance system performance. The SMTP service checks first for a name then an IP address. The brackets identify the value as an IP address. Therefore, the DNS lookup is bypassed.

Attempt direct delivery before sending to smart host

Select this option to try to deliver remote messages directly before forwarding them to the smart host server. The default is to send all remote messages to the smart host, not to try direct delivery.

Perform reverse DNS lookup on incoming messages

If you select this option, SMTP Server will try to verify that the client's IP address matches the host/domain submitted by the client in the EHLO/HELO command. If the reverse DNS lookup is successful, the RECEIVED header will remain intact. If the verification is unsuccessful, "unverified" appears after the IP address in the RECEIVED header of the message. If the DNS lookup fails, "RDNS failed" will appear in the RECEIVED header of the message. Because this feature verifies addresses for all incoming messages, its use could affect SMTP Server performance.