diff --git a/nixos/modules/services/mail/dovecot.nix b/nixos/modules/services/mail/dovecot.nix
index 135d3b277378..6057acc531a3 100644
--- a/nixos/modules/services/mail/dovecot.nix
+++ b/nixos/modules/services/mail/dovecot.nix
@@ -9,6 +9,8 @@ let
   baseDir = "/run/dovecot2";
   stateDir = "/var/lib/dovecot";
 
+  canCreateMailUserGroup = cfg.mailUser != null && cfg.mailGroup != null;
+
   dovecotConf = concatStrings [
     ''
       base_dir = ${baseDir}
@@ -314,17 +316,18 @@ in
            description = "Dovecot user";
            group = cfg.group;
          }
-      ++ optional cfg.createMailUser
-         { name = cfg.mailUser;
-           description = "Virtual Mail User";
+      ++ optional (cfg.createMailUser && cfg.mailUser != null)
+         ({ name = cfg.mailUser;
+            description = "Virtual Mail User";
+         } // optionalAttrs (cfg.mailGroup != null) {
            group = cfg.mailGroup;
-         };
+         });
 
     users.extraGroups = optional (cfg.group == "dovecot2")
       { name = "dovecot2";
         gid = config.ids.gids.dovecot2;
       }
-    ++ optional cfg.createMailUser
+    ++ optional (cfg.createMailUser && cfg.mailGroup != null)
       { name = cfg.mailGroup;
       };
 
diff --git a/nixos/release.nix b/nixos/release.nix
index f8d2e3145324..cbb566af7863 100644
--- a/nixos/release.nix
+++ b/nixos/release.nix
@@ -236,6 +236,7 @@ in rec {
   tests.containers-macvlans = callTest tests/containers-macvlans.nix {};
   tests.docker = hydraJob (import tests/docker.nix { system = "x86_64-linux"; });
   tests.docker-edge = hydraJob (import tests/docker-edge.nix { system = "x86_64-linux"; });
+  tests.dovecot = callTest tests/dovecot.nix {};
   tests.dnscrypt-proxy = callTest tests/dnscrypt-proxy.nix { system = "x86_64-linux"; };
   tests.ecryptfs = callTest tests/ecryptfs.nix {};
   tests.etcd = hydraJob (import tests/etcd.nix { system = "x86_64-linux"; });
diff --git a/nixos/tests/dovecot.nix b/nixos/tests/dovecot.nix
new file mode 100644
index 000000000000..3814855ed8e7
--- /dev/null
+++ b/nixos/tests/dovecot.nix
@@ -0,0 +1,64 @@
+import ./make-test.nix {
+  name = "dovecot";
+
+  machine = { pkgs, ... }: {
+    imports = [ common/user-account.nix ];
+    services.postfix.enable = true;
+    services.dovecot2.enable = true;
+    services.dovecot2.protocols = [ "imap" "pop3" ];
+    environment.systemPackages = let
+      sendTestMail = pkgs.writeScriptBin "send-testmail" ''
+        #!${pkgs.stdenv.shell}
+        exec sendmail -vt <<MAIL
+        From: root@localhost
+        To: alice@localhost
+        Subject: Very important!
+
+        Hello world!
+        MAIL
+      '';
+
+      testImap = pkgs.writeScriptBin "test-imap" ''
+        #!${pkgs.python3.interpreter}
+        import imaplib
+
+        with imaplib.IMAP4('localhost') as imap:
+          imap.login('alice', 'foobar')
+          imap.select()
+          status, refs = imap.search(None, 'ALL')
+          assert status == 'OK'
+          assert len(refs) == 1
+          status, msg = imap.fetch(refs[0], 'BODY[TEXT]')
+          assert status == 'OK'
+          assert msg[0][1].strip() == b'Hello world!'
+      '';
+
+      testPop = pkgs.writeScriptBin "test-pop" ''
+        #!${pkgs.python3.interpreter}
+        import poplib
+
+        pop = poplib.POP3('localhost')
+        try:
+          pop.user('alice')
+          pop.pass_('foobar')
+          assert len(pop.list()[1]) == 1
+          status, fullmail, size = pop.retr(1)
+          assert status.startswith(b'+OK ')
+          body = b"".join(fullmail[fullmail.index(b""):]).strip()
+          assert body == b'Hello world!'
+        finally:
+          pop.quit()
+      '';
+
+    in [ sendTestMail testImap testPop ];
+  };
+
+  testScript = ''
+    $machine->waitForUnit('postfix.service');
+    $machine->waitForUnit('dovecot2.service');
+    $machine->succeed('send-testmail');
+    $machine->waitUntilFails('[ "$(postqueue -p)" != "Mail queue is empty" ]');
+    $machine->succeed('test-imap');
+    $machine->succeed('test-pop');
+  '';
+}