+dkim_selector=$1
+if [ ! -n "${dkim_selector}" ]; then
+ echo "Give DKIM selector argument."
+ false
+fi
+
+# Set up DKIM key if necessary.
+mkdir -p /etc/dkimkeys/
+add_dkim_record=0
+if [ ! -f "/etc/dkimkeys/${dkim_selector}.private" ]; then
+ add_dkim_record=1
+ set +e
+ dpkg -s opendkim-tools &> /dev/null
+ preinstalled="$?"
+ set -e
+ if [ ! "${preinstalled}" -eq "0" ]; then
+ apt install -y opendkim-tools
+ fi
+ opendkim-genkey -s "${dkim_selector}"
+ mv "${dkim_selector}.private" /etc/dkimkeys/
+ if [ ! "${preinstalled}" -eq "0" ]; then
+ apt -y --purge autoremove opendkim-tools
+ fi
+fi
+
+# Link and adapt mail-server-specific /etc/ files.
+./hardlink_etc.sh mail
+sed -i "s/REPLACE_Domain_ECALPER/$(hostname -f)/g" /etc/opendkim.conf
+sed -i "s/REPLACE_Selector_ECALPER/${dkim_selector}/g" /etc/opendkim.conf
+
+# Some useful debconf selections.