1 files changed, 13 insertions, 8 deletions
diff --git a/mu4web/mu.py b/mu4web/mu.py
index 094db6a..09861af 100644
--- a/mu4web/mu.py
+++ b/mu4web/mu.py
@@ -19,22 +19,27 @@ from typing import (
 parser = BytesParser(policy=email.policy.default)
 
 
-def get_mail(id: str) -> email.message.Message:
-    """
-    Lookup email by Message-ID.
-
-    [Raises]
-        MuError
-    """
+def find_file(id: str) -> Optional[str]:
     cmd = subprocess.run(['mu', 'find', '-u', f'i:{id}',
                           '--fields', 'l'],
                          stdout=PIPE)
     filename = cmd.stdout.decode('UTF-8').strip()
 
+    if cmd.returncode == 4:
+        return None
     if cmd.returncode != 0:
         raise MuError(cmd.returncode)
+    return filename
 
-    with open(filename, "rb") as f:
+
+def get_mail(id: str) -> email.message.Message:
+    """
+    Lookup email by Message-ID.
+
+    [Raises]
+        MuError
+    """
+    with open(find_file(id), "rb") as f:
         mail = parser.parse(f)
     return mail