diff --git a/nixos/modules/services/mail/dovecot.nix b/nixos/modules/services/mail/dovecot.nix
index a2298152b02..1ccfb357750 100644
--- a/nixos/modules/services/mail/dovecot.nix
+++ b/nixos/modules/services/mail/dovecot.nix
@@ -405,7 +405,7 @@ in
         };
     } // optionalAttrs (cfg.createMailUser && cfg.mailUser != null) {
       ${cfg.mailUser} =
-        { description = "Virtual Mail User"; } // optionalAttrs (cfg.mailGroup != null)
+        { description = "Virtual Mail User"; isSystemUser = true; } // optionalAttrs (cfg.mailGroup != null)
           { group = cfg.mailGroup; };
     };
 
diff --git a/nixos/tests/dovecot.nix b/nixos/tests/dovecot.nix
index 1129e3b45d9..8913c2a6a7e 100644
--- a/nixos/tests/dovecot.nix
+++ b/nixos/tests/dovecot.nix
@@ -8,6 +8,8 @@ import ./make-test-python.nix {
       enable = true;
       protocols = [ "imap" "pop3" ];
       modules = [ pkgs.dovecot_pigeonhole ];
+      mailUser = "vmail";
+      mailGroup = "vmail";
     };
     environment.systemPackages = let
       sendTestMail = pkgs.writeScriptBin "send-testmail" ''