Solution: Users Don't Receive Email Sent by an Application

I don’t know much about Exchange, so was baffled when one of of one of our applications couldn’t send emails to an Exchange-based distribution list.

Symptoms

An application sends regular emails to numerous users, and this has been working for some time. A new Exchange based distribution list was set up so that a group of users could receive some of the emails.

  • Users in the distribution list receive the emails if the application was set to send them to their regular account.
  • If I send an email from my account, it reaches everyone in the distribution list.
  • Everyone else receives the mails from the application.
  • Nobody in the distribution list receives emails.

Diagnosis

The new distribution list is the only thing that has changes, so there was obviously something wrong with the list.
I asked one of our Exchange admins to investigate. Exchange message tracking suggested that the emails were being bounced back to the sending account.
Looking at the sender’s returned email revealed the problem with the distribution list.

Explanation

The distribution list was configured to only accept emails from authenticated users. Mails to the list that come from me get through because I’m logged in. However, the application doesn’t authenticate with Exchange when it sends emails. As a result they were being blocked by Exchange.

Solution

Change the settings on the distribution list so that it will receive emails from non-authenticated users.

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