diff --git a/hosts/containers/matemat/default.nix b/hosts/containers/matemat/default.nix
index b2e32a35..eb2e38cf 100644
--- a/hosts/containers/matemat/default.nix
+++ b/hosts/containers/matemat/default.nix
@@ -39,7 +39,7 @@
     enable = true;
     root = "nek0@c3d2.de";
     useSTARTTLS = true;
-    hostName = "mail.c3d2.de";
+    hostName = "mail.c3d2.de:587";
     domain = "matemat.hq.c3d2.de";
     settings = {
       hostname = "matemat.hq.c3d2.de";