# better late than never; I use Debian Buster (v10)
# turning off ipv6 solved this for me; clear the logs, turn off ipv6 on your system (optional), disable ipv6 in exim conf:
sudo pico /var/log/exim4/paniclog
# ctrl + "k" all the socket bind() to port 25 for address ::1 failed..., then ctrl...