SMTP Transport Tuning

This topic contains information about transport tuning on your servers. For Exchange 2000 Server customers, this section contains the same recommendations as previous Exchange 2000 Server performance documentation.

Mailroot Directory Location

In Exchange Server 2003, when messages arrive through SMTP, the data is written to a disk in the form of an NTFS file system file (specifically, an .eml file). By default, these files are written to a directory (<drive>:\Program Files\Exchsrvr\Mailroot) on the same disk partition where the Exchange Server 2003 binary files are installed.

In some scenarios, such as configuring a bridgehead or relay server, relocating the SMTP Mailroot directory to a faster disk partition may improve performance.

In Exchange Server 2003, you can use Exchange System Manager to move the Mailroot directory. For detailed instructions, see How to Move the Mailroot Directory in Exchange Server 2003.

SMTP MaxMessageObjects

Each message in an SMTP queue uses at least 4 KB of memory; therefore, you can experience low memory if the queue grows very large. Lowering this setting reduces the maximum number of messages that can reside in the queue, therefore decreasing the maximum memory footprint for SMTP. After the configured limit is reached, each SMTP connection made to the server returns with an out-of-memory error. For example, if this value is reduced to 10,000, SMTP refuses inbound mail after the queue reaches 10,000 messages.

You can set the MaxMessageObjects registry value to specify a number of messages that can exist in an SMTP queue. For detailed instructions, see How to Set the MaxMessageObjects Registry Value.