diff --git a/src/pretix/settings.py b/src/pretix/settings.py
index 4fac411ead..fdae85244d 100644
--- a/src/pretix/settings.py
+++ b/src/pretix/settings.py
@@ -221,7 +221,7 @@ MAIL_FROM_NOTIFICATIONS = config.get('mail', 'from_notifications', fallback=MAIL
 MAIL_FROM_ORGANIZERS = config.get('mail', 'from_organizers', fallback=MAIL_FROM)
 MAIL_CUSTOM_SENDER_VERIFICATION_REQUIRED = config.getboolean('mail', 'custom_sender_verification_required', fallback=True)
 MAIL_CUSTOM_SENDER_SPF_STRING = config.get('mail', 'custom_sender_spf_string', fallback='')
-MAIL_CUSTOM_SMTP_ALLOW_PRIVATE_NETWORKS = config.getboolean('mail', 'custom_smtp_allow_private_networks', fallback=False)
+MAIL_CUSTOM_SMTP_ALLOW_PRIVATE_NETWORKS = config.getboolean('mail', 'custom_smtp_allow_private_networks', fallback=DEBUG)
 EMAIL_HOST = config.get('mail', 'host', fallback='localhost')
 EMAIL_PORT = config.getint('mail', 'port', fallback=25)
 EMAIL_HOST_USER = config.get('mail', 'user', fallback='')