SMTP: Causes of Hangs on Mail Gateway to SMTP

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1. Postoffice (PO) and Gateway should be on the same physical network.
   
   Because the gateway's temporary files are written on the postoffice (M:\MAILDATA\SMTP\), and not its local hard disk, the performance of the gateway is dependent on file input/output. The most effective way to ensure fast file input/output is to have both the gateway and postoffice on the same physical network.
2. Use a Mail Relay Host for inbound SMTP mail.
   
   It is not mandatory to have Mail Relay Host configured for inbound mail, but it is highly recommended. Because the SMTP gateway is dependent on a DOS redirector, and the reliability of a UNIX to DOS connection is not as robust as the reliability of a UNIX to UNIX connection (UNIX is multithreaded; DOS is single threaded), it is recommended to control the required UNIX to DOS connection by storing all messages destine for MS Mail on a Host before they get forwarded to MS Mail.
   
   In other words, the Mail Administrators need to have as much control over the less reliable UNIX to DOS connection as possible. The optimum way to control this is by putting a Mail Relay Host on the same network segment as the gateway and PO server. Not only does this increase the reliability of the UNIX to DOS connection from a physical perspective, but it allows the Host to be configured to open/close the connections more effectively.
3. Have routers use static routing.
   
   If the Smart Host (Mail Relay Host) is not on the same network segment as the gateway and PO, then static routes should be configured on the router that separates the gateway and host. The IP addresses for the Gateway and the Smart Host should be added to the static table on the router.
   
   NOTE: Most routers use dynamic routing by default; a static table needs to be manually created and maintained.
4. Use a 16-bit Network Interface Card (NIC).
   
   You should use a 16-bit NIC to get fast file input/output. Additionally, it is recommended to use a 16-bit NIC with the RAM disabled.
5. Use one protocol per NIC (IPX/SPX).
   
   When the postoffice is on a Novell NetWare server and IPX/SPX is used to access the postoffice when TCP/IP is used to access the Host, it might be necessary to isolate each protocol on a separate NIC.