Increasing resources available to IMAP service


The IMAP service in MailEnable is designed to handle many concurrent connections. You might find though that IMAP responsiveness is decreasing when you have many hundreds of connections. This will show as a delayed response to any invalid command sent to the server using the method of testing IMAP described in This may happen if a lot of the connections are actually performing a command at the exact same time, such as listing messages. In this case, you may get better performance increasing the amount of resources that IMAP has available. 


The MailEnable IMAP service uses worker threads to handle connections. By default the number of threads allocated for this is 32. This can be increased. The IMAP service needs to be restarted to read the new setting. Note that this number is not the number of available connections, and will use more memory on your server. Increase the amount if the response time is slow. Windows will use a 1Mb of memory for each thread, so increase this in amounts of 50. Try to keep the value under 500. The Windows registry key to add is detailed below.

For 64bit Windows servers:

[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Mail Enable\Mail Enable\Services]
"Worker Thread Pool Size"=dword:00000020

For 32bit Windows servers:

[HKEY_LOCAL_MACHINE\SOFTWARE\Mail Enable\Mail Enable\Services]
"Worker Thread Pool Size"=dword:00000020


Class:HOWTO: Product Instructions
Revised:Wednesday, September 9, 2020