diff --git a/notify/sendmail.sh b/notify/sendmail.sh
index 3964e90..162b539 100644
--- a/notify/sendmail.sh
+++ b/notify/sendmail.sh
@@ -27,7 +27,7 @@ sendmail_send() {
 
   SENDMAIL_FROM="${SENDMAIL_FROM:-$(_readaccountconf_mutable SENDMAIL_FROM)}"
   if [ -z "$SENDMAIL_FROM" ]; then
-    SENDMAIL_FROM="$USER@$HOSTNAME"
+    SENDMAIL_FROM="$USER@$(hostname -f)"
     _info "The SENDMAIL_FROM is not set, so use the default value: $SENDMAIL_FROM"
   fi
   _saveaccountconf_mutable SENDMAIL_FROM "$SENDMAIL_FROM"