Remove ssmtp support and add From overwrite option

templates/nullmailer-inject.j2

@@ -0,0 +1,23 @@
+#!/bin/sh
+
+{% if mail.overwrite_from_header %}
+username="$(id -un 2> /dev/null || echo nobody)"
+
+excepted=0
+
+for excepted_user in {% for item in mail.overwrite_from_header_except_users %} {{ item|quote }} {% endfor %}; do
+	if [ "$username" = "$excepted_user" ]; then
+		excepted=1
+		break
+	fi
+done
+
+if [ "$excepted" = "0" ]; then
+	export NULLMAILER_NAME="${username} on $(hostname -f)"
+	export NULLMAILER_USER={{ mail.from.split('@')[0]|quote }}
+	export NULLMAILER_HOST={{ mail.from.split('@', 1)[1]|quote }}
+	export NULLMAILER_FLAGS=f
+fi
+{% endif %}
+
+exec /usr/bin/nullmailer-inject-bin "$@"