If your messaging system has stopped sending messages, there are a number of possible causes. This article will attempt to summarize some of the common reasons this can happen and provide solutions where possible.
Solution 1: Scheduler has stopped
The Core Messaging system uses the scheduler to send its messages. If the scheduler is stopped, messages will not send out. See our article on how to Configure the Scheduler to see how to resolve this problem.
Solution 2: Scheduler is running, but the messaging dispatch is failing or disabled
The Messaging Dispatch task is responsible for sending out messages. If that process is failing, there may be an incorrect setting involved. Our article titled Scheduler Task is not Running outlines a general process for troubleshooting any given scheduler task. Follow the steps in that article for the task called Messaging Dispatch.
Solution 3: Messaging is stalled due to SQL problems
The Messaging Dispatch uses SQL to store both its messages and its message queue. If the connection between the scheduler server and SQL server has been interrupted, there may be a mismatch between the contents of the two servers.
This problem will usually be accompanied by general site performance issues and extensive error logs.
The article Core Messaging Scheduler creating errors after upgrade walks you through clearing out the message queue on the SQL server.
Solution 4: SMTP issues
If messages were sending internally but not to outside recipients, the problem may be with the SMTP server responsible for sending your mail. Check with the SMTP server provider separately to make sure there are no ongoing issues with the server, and check the DNN Server Logs to see if there are SMTP errors that can shed more light on the problem.
This problem may also be caused by incorrectly-cached SMTP server information. See the article SMTP server not sending email messages for information on how to fix it.
Each article linked above contains its own testing information. Be sure to follow the testing information in those articles to ensure each fix is tested correctly. If the messaging system is working correctly, messages should be sending and receiving without generating errors.