Comment 2 for bug 1679833

As Rod's MR in the summary indicates, you can work around this superficially by forcing the install of sendmail.

The way this was handled in the past was to install the offending package separately and then manipulate it before installing the cert packages via cloud-init (for our stuff). This happened long ago with mysql being installed as a dependency of something else (mysql was never even used, it was just a dependency of a dependency of a dependency, IIRC).

Looking back in time, this is how it was handled before:

echo " Installing debconf-utils...";
      apt-get install -y debconf-utils;
      echo " Setting up and install mysql-server...";
      echo mysql-server mysql-server/root_password password insecure | debconf-set-selections;
      echo mysql-server mysql-server/root_password_again password insecure | debconf-set-selections;
      apt-get install -y mysql-server;

in the installcert bucket in curtin_userdata. I imagine something similar could be done here to automate choosing the "no configuration" option for postfix.

That said, we could also just as easily continue to force sendmail to be installed as well.