Apply @bitancer's suggestion

Co-authored-by: R. David Murray <rdmurray@bitdance.com>

Author: StanFromIreland

Doc/library/mailbox.rst

@@ -17,9 +17,10 @@ Supported mailbox formats are Maildir, mbox, MH, Babyl, and MMDF.
 
 .. warning::
 
- The :mod:`!mailbox` module is designed for use in trusted environments,
- where all inputs are provided by the local user and the underlying mailbox
- storage is accessible only to that user.
+   The :mod:`!mailbox` module is designed for use in trusted environments,
+   where data from untrusted sources is never passed to the module's API
+   calls and only trusted users have access to the filesystems accessible
+   to the module.
 
 .. seealso::