When an e-mail is undeliverable, for any number of reasons, it can get stuck in a queue. Occasionally, stuck messages can cause all other messages on your server to be queued, thus no mail can be sent from your server.
1) To manage your queue, find the Email menu.
2) Go to Mail Queue Manager.
Here is the Exim Mail Queue. As you can see, our queue has two messages in it. Yours may be empty, or it may have thousands of messages. Each message lists its size and time spent in the queue.
Delete a message, or Deliver Now with these two links. If the original delivery problems still exist, you probably will still not be able to send the message.
You can also Attempt to Deliver all messages in the Queue with this link.
3) Let's check out an individual message.
4) Here, you'll see detailed information about the message, its headers...
...and the message body, below.
5) Click Deliver Message Now to attempt delivery again.
As you can see, a failure message has appeared in the log. The destination hostname could not be resolved; the message still could not be sent.
6) Click here to Return to the Mail Queue.
The old message is no longer in the queue, but it has been replaced with a new error e-mail to the sender.
7) When all else fails, click here to Delete all messages in the Queue.
8) Confirm by clicking Delete All.
The messages have been removed from the queue.
This completes the tutorial. Now you can manage the mail queue whenever you need to do so.