It seems like I'm always having to force flush Exim. I don't know why. Mail gets queued up. I look at the logs. I don't get answers. I do the following and the mail goes out and everything is for for a while:
If I have too much stuff stuck in the queue and '-qff' is taking too long then I delete everything from the queue. This causes messages to be lost, but it clears stubborn problems:
exim -Mrm $(mailq|grep \<|cut -c 11-27)
This is from the Exim man page:
-q[q][i]ff... If ff is present, a delivery attempt is forced for every message, whether frozen or not.