diff --git a/nixos/tests/postfix.nix b/nixos/tests/postfix.nix
index 37ae76afec10..29e263cd7e78 100644
--- a/nixos/tests/postfix.nix
+++ b/nixos/tests/postfix.nix
@@ -11,7 +11,7 @@ import ./make-test-python.nix {
       enable = true;
       enableSubmission = true;
       enableSubmissions = true;
-      sslCACert = certs.ca.cert;
+      tlsTrustedAuthorities = certs.ca.cert;
       sslCert = certs.${domain}.cert;
       sslKey = certs.${domain}.key;
       submissionsOptions = {