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How-To: Troubleshoot outbound mail flow

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It has occur from time to time that domains are able to receive email but are not able to send outbound emails. There is a number of factors that can contribute to this issue from modus services not started to compromised accounts. Here are some troubleshooting steps that can be done to ensure mail flow is working.





Step 1:


  • Ensure that port 25 is able to relay outbound from your existing modus server. Open a command prompt from your modus server and attempt to telnet to any external domain on port 25. May i suggest telnet to on port 25. If you are able to connect and see a banner this indicates that port 25 is opened.

  • If an SMTP banner does not display or if you are unable to connect to via port 25, please verify your local firewall policies to ensure outbound mail flow is allowed. if this is not the case head to step 2.

Step 2:


  • Ensure if all modus services are running on the server, any service that is not running may cause mail flow issues or delay in email. If this is not the case head to step 3.


Step 3: 


  • Locate your spool directory within your modus console. The path can be found in modus under SYSTEM - SETTINGS

  • Copy that directory path into a windows explorer page where a list of folders will be displayed. One of those folders will be named DOMAINS.
  • Right click the domains folder and select PROPERTIES from the menu.

  • On the properties page be aware of the Contains label and the number of files listed.
  • If the number is greater than 500, this may indicate a spam attack or compromised account.



Step 4: 


  • In the spool directory in the domains folder, locate any domain listed of abnormal naming convention or bizarre format. This may indicate a compromised account ... ie (, etc.
  • go into one of these folder and see if any files are listed.
  • If a number of files are listed with the extension .DEF, this indicates that emails being sent to this domain have failed or is unable to reach its destination.



Step 5:


  • Double click to open any of the .DEF files found.
  • The content of the file may contain some information as listed below.
  • The main points of the .DEF file are highlighted below.
  • The TRY-NUMBER value indicates how many times the email attempted to resend itself.
  • The AUTH-LOGIN value indicates which user account authenticated to send the message.
  • The LAST-ERROR value indicates the reason as to why the email was not delivered.


Step 6:


  • After repeatedly performing STEP 4 and STEP 5 on different domain folders.
  • And if the content of the .DEF files seem to contain the same AUTH-LOGIN and LAST-ERROR info.
  • This is will a sure you that there is a compromised account, which can indeed cause the disruption of outbound mail flow.






  • Locate the culprits mailbox within your mail exchanger software and perform the following.
    • Change user account password\or disable account.
    • Rename the modus spool directory path found in STEP 3.
    • Restart all modus services in the console under SYSTEM - SERVICES.
    • Perform security scan on mail exchanger.
    • Perform security scan on clients end workstation.



  •  Locate the culprit mailbox within modusMail Console and perform the following.
    • Change user account password\or disable account.
    • Rename the modus spool directory path found in STEP 3.
    • Restart all modus services in the console under SYSTEM - SERVICES.
    • Perform security scan on modusMail server.
    • Perform security scan on clients end workstation.







Modified 9/5/2017
Keywords: outbound mail MTN
Article ID: 1969