Incoming Spool Directory is Backing Up


Product: ModusMail

Version & Build: All




Messages are backed up in the …\Vircom\ModusMail\Spool\Incoming folder and delivery to the users is taking a long time.



The SMTPDS (delivery service) is responsible for mail processing in the Incoming and Holding / Domains directories.  Messages waiting to be processed through Incoming include:

  • Mail from the outside world (Internet) waiting to be delivered to local mailboxes
  • Mail from local users waiting to be delivered to other local users and to the outside world (Internet)
  • Delivery failure notices or other internal postmaster warning messages generated by Modus


Causes and troubleshooting tips:

There are several possible reasons for delays in this part of the spool and this article includes a list of the most likely causes and specific configuration errors. 


1 - Postmaster's Inbox is full:

  • In the Console, go to Users – Properties – Info and select the Postmaster mailbox for the default (primary)
  • Check the Mailbox Size (# messages)
  • If there are 1000+ messages, in Windows Explorer, rename the Inbox folder (i.e. …Vircom\ModusMail\Mailbox\postmaster\Inbox)
  • In the Console, for the Postmaster account, go to Users – Preferences – Quotas and set all quotas to None
  • Stop and start the SMTPDS service
  • If the postmaster box is forwarding to a local email address, perform these steps for that address too

2 - The Spool\Domains\$local$ directory is backlogged:

  • Check if the drive containing the Mailbox directory is full and free up space, if necessary
  • Check if the C: drive is full, even if Modus is installed on another drive
    • A minimum of 500mg free space is required
  • Check the properties on the drive(s) containing the Mailbox and Spool directories
    • Disable the Indexing Service, which is turned on by default
      • Disable it on the drive properties directly and allow the change to propagate to the child objects (this can take a very long time) or  turn off the Indexing Service in Administrative Tools > Services (preferred)
  • If you use Generic (Registry) mailboxes, ensure that there is enough space in the Registry
    • Right-click the My Computer icon and select Properties
    • Click on Advanced > Performance Options> Change and verify the current and maximum registry size settings
  • If you use a database for authentication, check the following:
    • Is the database responding (i.e. is the SQL service running)?
    • Are there any performance problems on the database with CPU or memory consumption?  Check the Event Viewer & Task Manager.
    • Do you have any indexes or triggers set up on the database that call other tables or databases? If so, remove them.
  • Are you running a database trace or logging?  Go to the Data Sources (ODBC) and click on Tracing to stop any tracing.


3 - Mail Loops and Denial of Service (DoS) attacks:


The program may be experiencing multiple simultaneous mail loops that may be the result of a DoS attack.  While Modus is designed to discard any messages that cannot be processed when in a loop, multiple simultaneous loops or a directed spam attack can affect the server's performance.


  • In Windows Explorer, go to …\Vircom\ModusMail\Spool\Dead folder to check the contents
  • Multiple .msg and.txt files, with the same message IDs, indicates a mail looping problem
  • Open the .txt files to confirm the error ("mail loop has been detected")
  • Check the associated .msg file to see what address is having problems
  • To resolve this problem, in the Console, go to Users – Properties – General and select the user causing the problem
  • Remove the forwarding address from the user's setting or disable Don't leave a copy of a forward message in this mailbox and, instead, set a message lifetime of 1 day under Users – Preferences – Quotas


For DoS attacks:


Look for multiple delivery failure messages that appear to be generated by the same source address.  Proceed with one or more of the following:

  • Block that address in Security – Properties – Protocol Filter
  • Add that address in Security – Properties – Connections, click on Reject all incoming mail from...
  • Alternatively, you can create a custom sieve script


From a Command Prompt, run the netstat -a command to review all current connections to the server.  If there are multiple connections from questionable sources, block them using the Security options:

  • Go to Security – Properties – Connection Limits, enable Total number of simultaneous connections allowed from the same IP and set the limit