diff --git a/base-files/mail.conf b/base-files/mail.conf
index 0ffc1b1..28e24e6 100644
--- a/base-files/mail.conf
+++ b/base-files/mail.conf
@@ -1,6 +1,6 @@
 # This file is sourced by various scripts that need to send emails.
 
-case "${HOSTNAME#*.}" in
+case "$(hostname -d)" in
   afterdark.lan)
     EMAIL_DOMAIN="afterdark.org.uk"
     ;;