-# Everything should now be ready for installations.
-apt install -y postfix dovecot-imapd opendkim
-echo "TODO: Ensure a proper SPF entry for this system in your DNS configuration."
+# Everything should now be ready for installations. Note that we don't
+# strictly need dovecot-lmtpd, as postfix will deliver mail to /var/mail/USER
+# in any case, to be found by dovecot; we use it as a transport mechanism to
+# allow for sophisticated stuff like dovecot-side sieve filtering (installed
+# with dovecot-sieve).
+apt install -y -o Dpkg::Options::=--force-confold postfix dovecot-imapd dovecot-lmtpd dovecot-sieve opendkim
+echo "TODO: Ensure MX entry for your system in your DNS configuration."
+echo "TODO: Ensure a proper SPF entry for this system in your DNS configuration; something like 'v=spf1 mx -all' mapped to your host."