Softalk Mail Server Stops Sending Messages with a '450 Busy' Error Message

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Softalk Mail Server is no longer sending e-mails.

In the SMTPSND log files and in the Output window (SMTP Server) of the Softalk Mail Server Administrator, the following entry is appearing:

450 Busy

This error message is also returned to the client in an e-mail delivery failure notification.


In later versions of Softalk Mail Server, the number of SMTP threads has been limited to 50 in order to improve the overall performance of the application. In organizations with a large number of users or with a high amount of e-mail traffic, the limit of the available SMTP threads may be reached, thereby generating the 450 Busy error notifications.


The SMTP connection limit can be adjusted in the registry. To do so, please follow the steps below.

  1. Open the registry on the Softalk Mail Server server
  2. Navigate to HKLMSoftwareSoftalkWorkgroupMail
  3. If it doesn’t already exist, please create a new folder called Advanced
  4. Inside the newly created Advanced folder, create a new DWORD and name it smtpServerThrottle
  5. Assign this new registry key a decimal value based upon the following recommended equation ( n + ( n/100 * 25 ) where n is the current number of Softalk Mail Server mailboxes within your organization.
  6. Stop and restart Softalk Mail Server

More Info

What needs to be considered is the trade-off between the performance of Softalk Mail Server and the number of SMTP Threads that need to be available in order to serve requests; the more threads that are open the more performance can suffer as a result.

The recommended equation is a guideline rather than a rule. This should allow for the creation of a higher number of smtp threads to be available within an organization without having a noticable impact on the performance of the Softalk Mail Server server.

IMPORTANT: This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs.

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