export interface MessageAttachment {
    /**
     * When present, contains the ID of an external attachment that can be retrieved in a
     * separate messages.attachments.get request.
     * When not present, the entire content of the message part body is contained in the data field.
     */
    attachmentId: string;
    /**
     * Number of bytes for the message part data (encoding notwithstanding).
     */
    size: number;
    /**
     * The body data of a MIME message part as a base64url encoded string.
     * May be empty for MIME container types that have no message body or when the
     * body data is sent as a separate attachment. An attachment ID is present if the
     * body data is contained in a separate attachment.
     */
    data: string;
}