@silverbirder/rminc/dist/user/mail/mailMessage/iMailMessage.d.ts

rMinc is the Google Apps Script Library that register Mail in Calendar

/// <reference types="google-apps-script" />
export default interface IMailMessage {
    subject?: string;
    body?: string;
    date?: Date;
    getSubject(): string;
    getBody(): string;
    getDate(): Date | GoogleAppsScript.Base.Date;
}