Using startup switches in the MTA startup file, you can fine-tune the performance of TCP/IP links.
When using TCP/IP links between domains, you can control the number of inbound connections the MTA can establish for receiving messages.
Use the /tcpinbound switch in the MTA startup file to increase the maximum number of inbound connections the MTA can establish from the default of 40 to whatever setting meets the needs of your system. There is no maximum setting.
If the MTA is receiving more requests than it can accept, the sending MTAs must wait until a connection becomes available, which slows down message transfer. Each connection requires only about 20 KB. For example, if you configure the MTA to accept 600 connections, it would require approximately 12 MB of RAM. Although there is no maximum setting for inbound connections, this setting is adequate to handle very heavy usage. Use lower settings to conserve RAM or for lighter usage.
MTA Web Console
You can check the maximum number of TCP/IP connections that the MTA can start on the Configuration page under the TCP/IP Settings heading.
When using TCP/IP links, you can control how long the MTA waits for responses.
By default, the MTA waits 5 seconds for a response when trying to contact another MTA or a POA across a TCP/IP link. If no response is received from the other MTA or the POA, the sending MTA tries again three more times. If all four attempts fail, the MTA reports an error, then waits 10 minutes before it tries again.
When the MTA attempts to send messages to another MTA or a POA across a TCP/IP link, the sending MTA tries for 20 seconds before reporting an error.
On some networks, these wait intervals might not be sufficient, and the MTA might report an error when, by waiting longer, the needed connection or data transfer would be able to take place.
Use the /tcpwaitconnect switch in the MTA startup file to increase the number of seconds the MTA waits for a response from another MTA or a POA across a TCP/IP link.
Use the /tcpwaitdata switch in the MTA startup file to increase the number of seconds the MTA attempts to send messages to another MTA or a POA across a TCP/IP link.
MTA Web Console
You can check the current wait intervals on the Configuration page under the TCP/IP Settings heading.