@CreativeWolf, you also need to go to the services file, e.g. /etc/services and replace the lines that poppassd uses with these using the port 106 on TCP/UDP protocols):

(with # is considered a comment, the original lines from poppassd)

#poppassd 106/tcp # Eudora
#poppassd 106/udp
courierpassd 106/tcp
courierpassd 106/udp

Then do a restart to make sure that all services have being running properly.

I managed to fix it by installing courierpassd and the poppassd-change-password plugin of rainloop.