diff --git a/nix/sources.json b/nix/sources.json
index 906a4c5..654eb6a 100644
--- a/nix/sources.json
+++ b/nix/sources.json
@@ -60,13 +60,13 @@
         "url_template": "<repo>/-/archive/<rev>.tar.gz"
     },
     "nixos-mailserver": {
-        "branch": "nixos-21.05",
-        "ref": "nixos-21.05",
+        "branch": "nixos-21.11",
+        "ref": "nixos-21.11",
         "repo": "https://gitlab.com/simple-nixos-mailserver/nixos-mailserver",
-        "rev": "5675b122a947b40e551438df6a623efad19fd2e7",
-        "sha256": "1fwhb7a5v9c98nzhf3dyqf3a5ianqh7k50zizj8v5nmj3blxw4pi",
+        "rev": "6e3a7b2ea6f0d68b82027b988aa25d3423787303",
+        "sha256": "1i56llz037x416bw698v8j6arvv622qc0vsycd20lx3yx8n77n44",
         "type": "tarball",
-        "url": "https://gitlab.com/simple-nixos-mailserver/nixos-mailserver/-/archive/5675b122a947b40e551438df6a623efad19fd2e7.tar.gz",
+        "url": "https://gitlab.com/simple-nixos-mailserver/nixos-mailserver/-/archive/6e3a7b2ea6f0d68b82027b988aa25d3423787303.tar.gz",
         "url_template": "<repo>/-/archive/<rev>.tar.gz"
     },
     "nixpkgs": {