That means that there is a previous error and exim is just waiting to try again.
If you want to force the message to try again *now*, then you can run:
Code:
exim -M <message-ID>
where the <message-ID> is the set of characters in the logfile. Once you force it to try again, if it produces another error, the error will be right at the end of the /var/log/exim/mainlog so you can see why it failed the first time.
You have to find the error message for the cause...
If you want to see the error message, you can use the same:
exim -M <message-id>
method again, and this should create the error in the log again. Then, at the bottom of the /var/log/exim/mainlog file, you should see the error message. (or do "cat /var/log/exim/mainlog | grep <message-id>")