diff --git a/scripts/odysseus-mail b/scripts/odysseus-mail
index d4ce3ed..d90701a 100755
--- a/scripts/odysseus-mail
+++ b/scripts/odysseus-mail
@@ -107,6 +107,19 @@ def _q(name: str) -> str:
     return '"' + (name or "").replace("\\", "\\\\").replace('"', '\\"') + '"'
 
 
+def _split_recipients(value: str) -> list[str]:
+    return [r.strip() for r in (value or "").split(",") if r.strip()]
+
+
+def _recipient_list(to: str, cc: str = "", bcc: str = "") -> list[str]:
+    recipients = _split_recipients(to)
+    recipients.extend(_split_recipients(cc))
+    recipients.extend(_split_recipients(bcc))
+    if not recipients:
+        fail("at least one recipient is required")
+    return recipients
+
+
 # ─── list ────────────────────────────────────────────────────────────
 
 def cmd_list(args) -> None:
@@ -302,11 +315,7 @@ def cmd_send(args) -> None:
     outer["Date"] = datetime.utcnow().strftime("%a, %d %b %Y %H:%M:%S +0000")
     outer.attach(MIMEText(body, "plain", "utf-8"))
 
-    recipients = [r.strip() for r in args.to.split(",") if r.strip()]
-    if args.cc:
-        recipients.extend([r.strip() for r in args.cc.split(",") if r.strip()])
-    if args.bcc:
-        recipients.extend([r.strip() for r in args.bcc.split(",") if r.strip()])
+    recipients = _recipient_list(args.to, args.cc, args.bcc)
 
     if args.dry_run:
         emit({
diff --git a/tests/test_mail_cli_recipients.py b/tests/test_mail_cli_recipients.py
new file mode 100644
index 0000000..afe19f0
--- /dev/null
+++ b/tests/test_mail_cli_recipients.py
@@ -0,0 +1,57 @@
+import importlib.machinery
+import importlib.util
+import sys
+from pathlib import Path
+from types import ModuleType
+
+
+def _load_mail_cli(monkeypatch):
+    helpers = ModuleType("routes.email_helpers")
+    helpers._imap = object
+    helpers._get_email_config = lambda account=None: {}
+    helpers._decode_header = lambda value: value
+    helpers._extract_text = lambda msg: ""
+    helpers._extract_html = lambda msg: ""
+    helpers._list_attachments_from_msg = lambda msg: []
+
+    pollers = ModuleType("routes.email_pollers")
+    pollers._scheduled_poll_once = lambda: {}
+    pollers._run_auto_summarize_once = lambda **kwargs: ""
+
+    core_mod = ModuleType("core")
+    database_mod = ModuleType("core.database")
+    database_mod.SessionLocal = object
+    database_mod.EmailAccount = object
+
+    monkeypatch.setitem(sys.modules, "routes.email_helpers", helpers)
+    monkeypatch.setitem(sys.modules, "routes.email_pollers", pollers)
+    monkeypatch.setitem(sys.modules, "core", core_mod)
+    monkeypatch.setitem(sys.modules, "core.database", database_mod)
+
+    path = Path(__file__).resolve().parent.parent / "scripts" / "odysseus-mail"
+    loader = importlib.machinery.SourceFileLoader("odysseus_mail_cli_under_test", str(path))
+    spec = importlib.util.spec_from_loader(loader.name, loader)
+    module = importlib.util.module_from_spec(spec)
+    loader.exec_module(module)
+    return module
+
+
+def test_recipient_list_trims_to_cc_and_bcc(monkeypatch):
+    cli = _load_mail_cli(monkeypatch)
+
+    assert cli._recipient_list(" a@example.com, ", "b@example.com", " c@example.com ") == [
+        "a@example.com",
+        "b@example.com",
+        "c@example.com",
+    ]
+
+
+def test_recipient_list_rejects_empty_envelope(monkeypatch):
+    cli = _load_mail_cli(monkeypatch)
+
+    try:
+        cli._recipient_list(" , ", "", "")
+    except SystemExit as exc:
+        assert exc.code == 1
+    else:
+        raise AssertionError("expected empty recipient list to exit")