diff --git a/mail/postfix/src/opnsense/service/templates/OPNsense/Postfix/main.cf b/mail/postfix/src/opnsense/service/templates/OPNsense/Postfix/main.cf
index 7ad6a1c27..5ce384efa 100644
--- a/mail/postfix/src/opnsense/service/templates/OPNsense/Postfix/main.cf
+++ b/mail/postfix/src/opnsense/service/templates/OPNsense/Postfix/main.cf
@@ -157,6 +157,7 @@ relayhost = {{ OPNsense.postfix.general.relayhost }}
 smtp_sasl_auth_enable = yes
 smtp_sasl_password_maps = hash:/usr/local/etc/postfix/smtp_auth
 smtp_sasl_security_options =
+smtp_sasl_mechanism_filter = !gssapi, !external, static:all
 {% endif %}
 
 {% if helpers.exists('OPNsense.postfix.general.permit_sasl_authenticated') and OPNsense.postfix.general.permit_sasl_authenticated == '1' %}