diff --git a/.hydra/declarative-jobsets.nix b/.hydra/declarative-jobsets.nix
index f96d5ba..43c9fa8 100644
--- a/.hydra/declarative-jobsets.nix
+++ b/.hydra/declarative-jobsets.nix
@@ -88,6 +88,33 @@ let
         };
       };
     };
+    "nixos-21.05" = {
+      description = "Build the nixos-21.05 branch of Simple NixOS MailServer";
+      checkinterval = "60";
+      enabled = "1";
+      nixexprinput = "snm";
+      nixexprpath = ".hydra/default.nix";
+      schedulingshares = 100;
+      enableemail = false;
+      emailoverride = "";
+      keepnr = 3;
+      hidden = false;
+      type = 0;
+      inputs = {
+        # This is only used to allow Niv to use pkgs.fetchzip which is
+        # required because of Hydra restricted evaluation mode.
+        nixpkgs = {
+          value = "https://github.com/NixOS/nixpkgs b6eefa48d8e10491e43c0c6155ac12b463f6fed3";
+          type = "git";
+          emailresponsible = false;
+        };
+        snm = {
+          value = "https://gitlab.com/simple-nixos-mailserver/nixos-mailserver master";
+          type = "git";
+          emailresponsible = false;
+        };
+      };
+    };
   };
 
 in {
diff --git a/README.md b/README.md
index e680154..4ef7d2a 100644
--- a/README.md
+++ b/README.md
@@ -8,6 +8,10 @@
 For each NixOS release, we publish a branch. You then have to use the
 SNM branch corresponding to your NixOS version.
 
+* For NixOS 21.05
+   - Use the [SNM branch `nixos-21.05`](https://gitlab.com/simple-nixos-mailserver/nixos-mailserver/-/tree/nixos-21.05)
+   - [Documentation](https://nixos-mailserver.readthedocs.io/en/nixos-21.05/)
+   - [Release notes](https://nixos-mailserver.readthedocs.io/en/nixos-21.05/release-notes.html#nixos-21-05)
 * For NixOS 20.09
    - Use the [SNM branch `nixos-20.09`](https://gitlab.com/simple-nixos-mailserver/nixos-mailserver/-/tree/nixos-20.09)
    - [Documentation](https://nixos-mailserver.readthedocs.io/en/nixos-20.09/)
@@ -15,7 +19,7 @@ SNM branch corresponding to your NixOS version.
 * For NixOS unstable
    - Use the [SNM branch `master`](https://gitlab.com/simple-nixos-mailserver/nixos-mailserver/-/tree/master)
    - [Documentation](https://nixos-mailserver.readthedocs.io/en/latest/)
-   - This branch is currently supporting the NixOS release 20.09 but
+   - This branch is currently supporting the NixOS release 21.05 but
      we could remove this support on any NixOS unstable breaking
      change.
 
@@ -79,7 +83,7 @@ D9FE 4119 F082 6F15 93BD  BD36 6162 DBA5 635E A16A
 
 ```nix
    { config, pkgs, ... }:
-   let release = "nixos-20.09";
+   let release = "nixos-21.05";
    in {
      imports = [
        (builtins.fetchTarball {
diff --git a/docs/release-notes.rst b/docs/release-notes.rst
index 561a40c..fce2abf 100644
--- a/docs/release-notes.rst
+++ b/docs/release-notes.rst
@@ -1,6 +1,16 @@
 Release Notes
 =============
 
+NixOS 21.05
+-----------
+
+- New `fullTextSearch` option to search in messages (based on Xapian)
+  (`Merge Request <https://gitlab.com/simple-nixos-mailserver/nixos-mailserver/-/merge_requests/212>`__)
+- Flake support
+  (`Merge Request <https://gitlab.com/simple-nixos-mailserver/nixos-mailserver/-/merge_requests/200>`__)
+- New `openFirewall` option defaulting to `true`
+- We moved from Freenode to Libera Chat
+
 NixOS 20.09
 -----------
 
diff --git a/nix/sources.json b/nix/sources.json
index 2d2d79a..1edeea8 100644
--- a/nix/sources.json
+++ b/nix/sources.json
@@ -18,6 +18,18 @@
         "url": "https://github.com/NixOS/nixpkgs/archive/b6eefa48d8e10491e43c0c6155ac12b463f6fed3.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
+    "nixpkgs-21.05": {
+        "branch": "release-21.05",
+        "description": "Nix Packages collection",
+        "homepage": "",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "3776ceb792907ddebd7d2603778c7f106fabfb08",
+        "sha256": "10wmmnf5scmrnf1knc31yhwlrq720n3k26j44daqal4shqxhr2vk",
+        "type": "tarball",
+        "url": "https://github.com/nixos/nixpkgs/archive/3776ceb792907ddebd7d2603778c7f106fabfb08.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
     "nixpkgs-unstable": {
         "branch": "nixos-unstable",
         "description": "A read-only mirror of NixOS/nixpkgs tracking the released channels. Send issues and PRs to",
diff --git a/tests/default.nix b/tests/default.nix
index 10aba18..68f2053 100644
--- a/tests/default.nix
+++ b/tests/default.nix
@@ -29,6 +29,7 @@ let
   releaseNames = [
     "nixpkgs-unstable"
     "nixpkgs-20.09"
+    "nixpkgs-21.05"
   ];
 
   testNames = [