diff --git a/flake.lock b/flake.lock
index cff6b45..a2aec8f 100644
--- a/flake.lock
+++ b/flake.lock
@@ -90,11 +90,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1645244400,
-        "narHash": "sha256-o7KCd6ySFZ9/LbS62aTeuFmBWtP7Tt3Q3RcNjYgTgZU=",
+        "lastModified": 1645915321,
+        "narHash": "sha256-trvB0bthXbPgga5sE93p+k6olVOfZgsR9BTlAaJJs20=",
         "owner": "nix-community",
         "repo": "home-manager",
-        "rev": "0232fe1b75e6d7864fd82b5c72f6646f87838fc3",
+        "rev": "1d90b6065a0e8713b21cffd7af4f03e31894ae8b",
         "type": "github"
       },
       "original": {
@@ -126,11 +126,11 @@
       },
       "locked": {
         "dir": "contrib",
-        "lastModified": 1645221341,
-        "narHash": "sha256-01YUM9KnYxdzJoP8cs+2c+RVe40bsUSH3wVDmv3V9bU=",
+        "lastModified": 1645791029,
+        "narHash": "sha256-kXtr8uXR01drLnPDtqPZO0M2vY9wHVW0Iu3h1qlHKSI=",
         "owner": "neovim",
         "repo": "neovim",
-        "rev": "5cb45dffba730d0009d4c4d6b26efaa994727e2d",
+        "rev": "005a7aa1670841dfdffb7559161a7d37d6c14bc4",
         "type": "github"
       },
       "original": {
@@ -149,11 +149,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1645258396,
-        "narHash": "sha256-2avNcS2USBhH97we0SGgxljipD5hW+zrIt0OvH8PBYE=",
+        "lastModified": 1645863214,
+        "narHash": "sha256-RFI3GZLvSa7hQTlB/3oX7anM4d3ftWCpqWBrE17OUZA=",
         "owner": "nix-community",
         "repo": "neovim-nightly-overlay",
-        "rev": "61479c974a76d8f8ea0e9d45dca70aa42a48176e",
+        "rev": "9a5300fb01ef2eb5013f932913e8e7d5d96e4e9d",
         "type": "github"
       },
       "original": {
@@ -164,11 +164,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1644525281,
-        "narHash": "sha256-D3VuWLdnLmAXIkooWAtbTGSQI9Fc1lkvAr94wTxhnTU=",
+        "lastModified": 1645433236,
+        "narHash": "sha256-4va4MvJ076XyPp5h8sm5eMQvCrJ6yZAbBmyw95dGyw4=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "48d63e924a2666baf37f4f14a18f19347fbd54a2",
+        "rev": "7f9b6e2babf232412682c09e57ed666d8f84ac2d",
         "type": "github"
       },
       "original": {
@@ -180,11 +180,11 @@
     },
     "nixpkgs-21_05": {
       "locked": {
-        "lastModified": 1625692408,
-        "narHash": "sha256-e9L3TLLDVIJpMnHtiNHJE62oOh6emRtSZ244bgYJUZs=",
+        "lastModified": 1642244250,
+        "narHash": "sha256-vWpUEqQdVP4srj+/YLJRTN9vjpTs4je0cdWKXPbDItc=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "c06613c25df3fe1dd26243847a3c105cf6770627",
+        "rev": "0fd9ee1aa36ce865ad273f4f07fdc093adeb5c00",
         "type": "github"
       },
       "original": {
@@ -195,11 +195,11 @@
     },
     "nixpkgs-21_11": {
       "locked": {
-        "lastModified": 1638371214,
-        "narHash": "sha256-0kE6KhgH7n0vyuX4aUoGsGIQOqjIx2fJavpCWtn73rc=",
+        "lastModified": 1645652565,
+        "narHash": "sha256-yVQN2Wi8xSSpuj6JTck/6IOJ40hNvmoReMvFY86xd9w=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "a640d8394f34714578f3e6335fc767d0755d78f9",
+        "rev": "4275a321beab5a71872fb7a5fe5da511bb2bec73",
         "type": "github"
       },
       "original": {
@@ -210,11 +210,11 @@
     },
     "nixpkgs_2": {
       "locked": {
-        "lastModified": 1645010845,
-        "narHash": "sha256-hO9X4PvxkSLMQnGGB7tOrKPwufhLMiNQMNXNwzLqneo=",
+        "lastModified": 1645652565,
+        "narHash": "sha256-yVQN2Wi8xSSpuj6JTck/6IOJ40hNvmoReMvFY86xd9w=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "2128d0aa28edef51fd8fef38b132ffc0155595df",
+        "rev": "4275a321beab5a71872fb7a5fe5da511bb2bec73",
         "type": "github"
       },
       "original": {
@@ -226,11 +226,11 @@
     },
     "nur": {
       "locked": {
-        "lastModified": 1645311869,
-        "narHash": "sha256-Fij3yW90GzETuJ4q26WlaDU5w4GF1G2uMLIZhLiv5xM=",
+        "lastModified": 1645915960,
+        "narHash": "sha256-uVNTEKxXIUja2yJkBMrN1W9O9yqO9eGt0PvWtV9C8rc=",
         "owner": "nix-community",
         "repo": "NUR",
-        "rev": "a49f87e5f79d1133eab0e489d85d45ed340faa49",
+        "rev": "a54d798dc6fd8f772002f28b05f9686f6dc93afc",
         "type": "github"
       },
       "original": {
@@ -271,6 +271,7 @@
       },
       "original": {
         "owner": "simple-nixos-mailserver",
+        "ref": "nixos-21.11",
         "repo": "nixos-mailserver",
         "type": "gitlab"
       }
@@ -282,11 +283,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1644599065,
-        "narHash": "sha256-oFLRb9p954wiUGn8iU5wOCY/7yBrT4Xvg7Ew07MvSKs=",
+        "lastModified": 1645891244,
+        "narHash": "sha256-Pu3a97Zn0PpWi/prTyD9TulCmxyeVnlqofor+yScRD8=",
         "owner": "Mic92",
         "repo": "sops-nix",
-        "rev": "fc22eff3205e9742c1b0fd229c267bf237f0c43e",
+        "rev": "afb0d686dced029ea720c466f693c12ebfd4107b",
         "type": "github"
       },
       "original": {
@@ -297,11 +298,11 @@
     },
     "unstable": {
       "locked": {
-        "lastModified": 1644525281,
-        "narHash": "sha256-D3VuWLdnLmAXIkooWAtbTGSQI9Fc1lkvAr94wTxhnTU=",
+        "lastModified": 1645433236,
+        "narHash": "sha256-4va4MvJ076XyPp5h8sm5eMQvCrJ6yZAbBmyw95dGyw4=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "48d63e924a2666baf37f4f14a18f19347fbd54a2",
+        "rev": "7f9b6e2babf232412682c09e57ed666d8f84ac2d",
         "type": "github"
       },
       "original": {
diff --git a/flake.nix b/flake.nix
index 132577e..1a9258b 100644
--- a/flake.nix
+++ b/flake.nix
@@ -32,7 +32,7 @@
     };
 
     simple-nixos-mailserver = {
-      url = "gitlab:simple-nixos-mailserver/nixos-mailserver";
+      url = "gitlab:simple-nixos-mailserver/nixos-mailserver/nixos-21.11";
       inputs.nixpkgs.follows = "nixpkgs";
     };