how to fix it:
Okay so I'll just add this to my /etc/courier/imapd:
IMAPACCESSFILE=${sysconfdir}/imapaccess
Problem solved. Packages install fine now.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=815956
** Bug watch added: Debian Bug tracker #815956
Status changed to 'Confirmed' because the bug affects multiple users.
** Changed in: courier (Ubuntu)
Status: New => Confirmed
--
You received this bug notification because you are a member of Ubuntu
Bugs, which is subscribed to Ubuntu.
https://bugs.launchpad.net/bugs/1735092
Title:
** Tags removed: need-duplicate-check
--
You received this bug notification because you are a member of Ubuntu
Bugs, which is subscribed to Ubuntu.
https://bugs.launchpad.net/bugs/1735092
Title:
package courier-mta 0.78.0-2 failed to install/upgrade: subprocess
installed post-installation
