Comment 7 for bug 1531299

happened to me, I think I fixed it just editing the line

those variables are not initializated, so I thought adding an equals symbol could solve it, and it does

sudo gedit /etc/postfix/main.cf

find: "permit_sasl_authenticated,permit_mynetworks,reject_unauth_destination"

add an equals symbol at the end: "permit_sasl_authenticated,permit_mynetworks,reject_unauth_destination ="

then:

sudo apt-get update && sudo dpkg --configure -a && sudo apt-get install -f && sudo apt-get dist-upgrade && sudo apt-get upgrade && sudo apt-get autoremove && sudo apt-get clean && sudo apt-get autoclean