When installing courier-imap, it creates /etc/pam.d/pop3 and /etc/pam.d/imap. Then when installing postfix, which requires mailbase, there is a problem. mailbase has it own /etc/pam.d files and complains about those from courier-imap. Probably the best way out of that problem is to remove those files from courier-imap installation and add mailbase requirement.
*** This bug has been marked as a duplicate of 79240 ***