Attachment File Validation And Path Sanitization

** - This server enables users to send emails through various email providers, including Gmail, Outlook, Yahoo, Sina, Sohu, 126, 163, and QQ Mail. It also supports attaching files from specified directories, making it easy to upload attachments along with the email content.

Unique: Implements path validation using pathlib to ensure attachment files are within the configured directory boundary, preventing directory traversal attacks while maintaining clear error messages.

vs others: More secure than unrestricted file access and simpler than full filesystem permission systems, though less flexible than OS-level access controls.