diff --git a/docs/admin.md b/docs/admin.md
index 027bec7..dd7b905 100644
--- a/docs/admin.md
+++ b/docs/admin.md
@@ -7,6 +7,9 @@ Please do **not** use the standard Linux commands (e.g., `useradd`, `adduser`, .
 The script is interactive and allows to add, remove, and edit users.
 Please run `sudo userctl --help` for more information.
 
+Users on this server are identified by their university email address.
+Thus, `userctl` expects the full email address as argument.
+
 ## Process Management
 
 Some users may forget to stop their processes or block all GPUs at once.
diff --git a/modules/userctl.py b/modules/userctl.py
index a4cfe9c..7e979c9 100644
--- a/modules/userctl.py
+++ b/modules/userctl.py
@@ -25,7 +25,9 @@ def run_cmd(cmd: Sequence[str], **kwargs) -> str:
 
 def check_email(user: str):
     if not user.endswith("@uni-trier.de"):
-        raise typer.BadParameter("Only university mail addresses are allowed")
+        raise typer.BadParameter(
+            "Please provide the university email address, the script determines the username automatically"
+        )
 
     return user.split("@")[0]