diff --git a/mastus/mail.nix b/mastus/mail.nix
index b11e60d..2edd9fc 100644
--- a/mastus/mail.nix
+++ b/mastus/mail.nix
@@ -38,6 +38,14 @@
       smtpd_sasl_path = private/auth
       smtpd_sasl_auth_enable = yes
       smtpd_tls_auth_only = yes
+
+      # Do not send spam bounces
+      # http://www.postfix.org/ADDRESS_VERIFICATION_README.html
+      smtpd_recipient_restrictions =
+        permit_mynetworks permit_sasl_authenticated
+        reject_unauth_destination
+        reject_unknown_recipient_domain
+        reject_unverified_recipient
     '';
 
     extraMasterConf = ''