diff --git a/setup/mail-dovecot.sh b/setup/mail-dovecot.sh
index 978cba2..e4fbf16 100755
--- a/setup/mail-dovecot.sh
+++ b/setup/mail-dovecot.sh
@@ -203,5 +203,8 @@ chown -R mail.mail $STORAGE_ROOT/mail/sieve
 ufw_allow imaps
 ufw_allow pop3s
 
+# Allow the Sieve port in the firewall.
+ufw_allow sieve
+
 # Restart services.
 restart_service dovecot