Hi everyone. I have had the same problem on my Ubuntu installation and have after a few days of searching down wrong tracks found the solution.
The problem is, at least in Ubuntu, that authlib support is absent in the courier-maildrop package. Once I found out that this was my problem, I was able to get it to work by removing the courier-maildrop
package and instead install the standalone maildrop
sudo apt-get remove courier-maildrop
sudo apt-get install maildrop
I don't know where else I need to post this solution, someone please direct me. I am a newbee to this site.
And by the way. WOW! This is a great product! :-)