async save(mailEvent) {
        await this.#MailEventModel.add({
            id: mailEvent.id,
            type: mailEvent.type,
            message_id: mailEvent.messageId,
            recipient: mailEvent.recipient,
            occurred_at: new Date(mailEvent.timestampMs)
        });
    }
@param {MailEvent} mailEvent
@returns {Promise<void>}