Args:
        to: Recipient email address
        subject: Email subject
        body: Email body content
        is_html: Whether body is HTML (default: False)
        smtp_config: Optional SMTP configuration override with:
            - host: SMTP server hostname
            - port: SMTP server port
            - secure: Use SSL/TLS
            - username: Auth username
            - password: Auth password
            - from_email: Sender email address
            Falls back to environment variables if not provided.

    Returns:
        Success message or error message
    

    Args:
        email: Email message details including:
            - to: Recipient email address(es) (string or list)
            - cc: CC email address(es) (optional, string or list)
            - bcc: BCC email address(es) (optional, string or list)
            - subject: Email subject
            - text: Plain text email body (optional)
            - html: HTML email body (optional)
            - attachments: List of attachments (optional), each with:
                - path: Local file path to attach (preferred)
                - content: Base64-encoded file content (alternative to path)
                - filename: Override filename (auto-derived from path if omitted)
                - mime_type: MIME type override (optional)
        smtp_config: Optional SMTP configuration override with:
            - host: SMTP server hostname
            - port: SMTP server port
            - secure: Use SSL/TLS
            - username: Auth username
            - password: Auth password
            - from_email: Sender email address

    Returns:
        Success message or error message
    

    Args:
        smtp_config: Optional SMTP configuration override with:
            - host: SMTP server hostname
            - port: SMTP server port
            - secure: Use SSL/TLS
            - username: Auth username
            - password: Auth password
            - from_email: Sender email address
            Falls back to environment variables if not provided.

    Returns:
        Connection test result or error message
    

    Messages are read with BODY.PEEK and remain unread by default. Use
    ``from_address`` or ``subject_contains`` to narrow the result.
    

    The recipient defaults to ``notification.to`` in config.json. Use
    ``to`` only when a one-off recipient override is needed.
    

    The recipient defaults to ``notification.to`` in config.json. The
    email asks the recipient to reply with “批准” or “拒绝”.