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SMTP Server

SMTP Requirement:

Requirements for SMTP Server setup is identical to those of IIS. TCP/IP is definitely needed. NetBIOS name to IP address resolution (WINS/LMHOSTS) and hostname to IP address resolution (DNS/HOSTS) are needed to. Whether NTFS or FAT used is not immediately important for installation. NTFS is required for better local security.

SMTP Domain

On SMTP servers, domains are used to organize messages for delivery. Each SMTP site has at least one domain known as the default domain. You can add domains by creating them and configuring them as local domains or remote domains. You can delete any domains but the default domains.

A local domain is a domain that is served by the local SMTP server. This domain has an entry in the DNS table. When a message arrive, the message is put inside a local Drop folder.

A remote domain is a domain where there is no Drop folder on the local SMTP server. Mail addressed to remote server are forwarded to the SMTP server specified for that domain. The SMTP uses DNS entries to locate the remote domain SMTP server.

Smart Host is used to designate a server through which to route all outgoing messages.

Masquerade Domain is used to replace any local domain used in any From lines in the header, or Mail From lines in the protocol with a different domain name. For example, if I want my SMTP mail to appear coming from another domain.

SMTP Performance

You can increase SMTP performance by limiting the Number of Messages Per Connection, using smart headers and disabling Reverse DNS Lookup .

a) Limit Number of Messages Per Connection

This option enables you to limit the number of messages sent in a single connection. It also provides a method to improve system performance by allowing the use of multiple connections to deliver messages to a remote domain. Once the set limit is reached, a new connection is automatically opened and the transmission continues until all messages are delivered.

For example, you commonly send a large number of messages to a certain remote domains, reduce Maximum number of outbound messages per connection (by default 20). As a result, when sending 100 messages in one session, SMTP Service could be sending in 5 simultaneous connections (100/20). Message delivery would be faster, because fewer messages are delivered simultaneously, instead of in one long stream over one connection.

To determine a value for the limit, review the Messages Sent/sec performance counter for the SMTP Server object in Performance Monitor. The Maximum number of outbound messages per connection value should be less than the value indicated by the performance counter. If the counter indicates a value of 30, and you set your maximum connections to 50, no simultaneous connection would be opened because the server wouldn’t exceed 30 messages per second. It would work as though the messages were sent in one long stream over one connection. This setting affects outgoing messages only. You can use it to increase your server output speed, but it has no effect on the rate that other servers process incoming messages.

b) Smart Host

You can route all outgoing messages for remote domains through a smart host instead of sending them directly to the domain. This enables you to 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 once 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. 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.

You can identify the smart host by a string or an IP address. If you use an IP address, enclose it in brackets to increase system performance. Microsoft SMTP Service checks first for a string, then an IP address. The brackets identify the value as an IP address, so the string analysis is bypassed.

c) Disable Reverse DNS Lookup

If you select this option, Microsoft SMTP Service can verify that the IP address for the domain in the From line matches the originating IP address noted in the header. This address confirms that the message originated from the computer and the domain listed in the From field. If the reverse DNS lookup is successful, the domain name for the IP address is inserted in the Received header field. If the process is unsuccessful, only the IP address is included. Because this feature verifies addresses for all incoming messages, its use could affect Microsoft SMTP Service performance.

SMTP Security

Your main office and branch offices are connected through the Internet. You would like toconfigure secure e-mail. There are two main strategies: implement SSL or PPTP. If you implement PPTP, it will only ensure that your communication is secure and not tapped by somebody else. Using SSL make sure that the mail is actually sent by the right person. Therefore SSL is more secure in this case. You will need to configure a remote domain for every remote offices before specifying SSL.

Retry Attempts and Intervals

Determines how many times to resend a message, and at what intervals, before the message is considered undeliverable.

If a message cannot be delivered on the first attempt, Microsoft SMTP Service sends it again from the Queue directory after a specified time. You can set the interval between delivery attempts. You can also designate the number of times to attempt to deliver a message. After the limit is reached, the message is returned to the sender with an NDR and copies of the message and NDR are sent to the location you designate. The NDR is placed in the Queue directory and goes through the same delivery process as messages. When the NDR reaches the maximum number of retry attempts, the NDR and message are sent to the Badmail directory.

If the Local Disk Queue Length and the Remote Disk Queue Length performance counters have values of 0, it indicates that messages are being delivered immediately upon receipt. If the values are higher, it indicates that there is a delay.

If the Local Retry Queue Length and Remote Retry Queue Length have high values, it indicates that messages cannot be delivered. Open the .rtr files to determine what is causing the problem.

For example, if a remote server is down, the remote retry queue length may have a high value and .rtr files in the Queue directory might include the error message "Host not found."

If you experience high local queue retry daily, you need reduce the local query retry interval. By default, the interval is 60 minutes. This means that SMTP server will retry sending the mail every 1 hour until the maximum retry value is reached.

Your SMTP users might also be complaining that it takes too long to get "Undeliverable" messages back - about 48 hours. Reduce Local Queue Retry interval.

The Maximum Hop Count indicates how many server does the mail needs to be re-routed before the mail will be sent back to the sender with an NDR (non-delivery report). The default is 15 hops.



Wednesday, December 03, 2003