I don't think this is the exim config at all, but rather postfix.
Note that this doesn't change much; you'd want to preseed the MTA configuration in debian-cd in this file:
data/xenial/preseed/ubuntu-server/ubuntu-server.seed
For postfix, this means setting postfix/main_mailer_type to the value you want for No configuration.
In any case, this is not a debian-installer bug; and at most a bug in the seed or in debian-cd. Assigning to debian-cd for now.
I don't think this is the exim config at all, but rather postfix.
Note that this doesn't change much; you'd want to preseed the MTA configuration in debian-cd in this file: preseed/ ubuntu- server/ ubuntu- server. seed
data/xenial/
For postfix, this means setting postfix/ main_mailer_ type to the value you want for No configuration.
In any case, this is not a debian-installer bug; and at most a bug in the seed or in debian-cd. Assigning to debian-cd for now.