diff --git a/ubuntu-postfix-setup.sh b/ubuntu-postfix-setup.sh
index bb8aa53..4f67c4b 100644
--- a/ubuntu-postfix-setup.sh
+++ b/ubuntu-postfix-setup.sh
@@ -60,3 +60,12 @@ sudo certbot certonly --standalone --rsa-key-size 4096 --agree-tos --preferred-c
 
 # test 
 # echo "This is the body of an encrypted email" | mail -s "This is the subject line" root
+
+
+
+# dkim setup
+# ref: https://www.linuxbabe.com/mail-server/setting-up-dkim-and-spf
+apt install opendkim opendkim-tools
+gpasswd -a postfix opendkim
+vim /etc/opendkim.conf
+# ...