diff --git a/hosts/containers/matemat/default.nix b/hosts/containers/matemat/default.nix
index 0782dd38..b2e32a35 100644
--- a/hosts/containers/matemat/default.nix
+++ b/hosts/containers/matemat/default.nix
@@ -41,6 +41,9 @@
     useSTARTTLS = true;
     hostName = "mail.c3d2.de";
     domain = "matemat.hq.c3d2.de";
+    settings = {
+      hostname = "matemat.hq.c3d2.de";
+    };
   };
 
   security.acme = {