Troubleshooting Mail Flow Issues

Situation – You are experiencing issues with your mail flow, such as delayed delivery of messages, missing messages, or users unable to deliver or receive messages.

Solution – These are all questions that you should use as a basic guideline in attempting to determine the cause of an issue.

Basic Mail Flow Troubleshooting

Before beginning to troubleshoot, we recommend gathering some basic information about the problem. Taking a few minutes to better understand exactly how the mail flow issue is impacting the organization can narrow down possible causes of the problem, and may reduce troubleshooting time. Some key questions to answer are:


  • Are all of the users affected by the problem, or does the problem only impact some users?
  • If only some users are affected, then what do those users have in common with one another? Are all of their mailboxes on the same server?

Scope Of Impact

  • Does the problem occur with all mail flow, or is it limited to a specific type of mail, such as mail coming in from the Internet?

Consistency And Timing

  • When did the problem start? Did any other significant events occur around that time, such as a patch being applied, or a piece of hardware failing?