async getEmailId(providerId) {
        if (this.providerIdEmailIdMap[providerId]) {
            return this.providerIdEmailIdMap[providerId];
        }

        const {emailId} = await this.#db.knex('email_batches')
            .select('email_id as emailId')
            .where('provider_id', providerId)
            .first() || {};

        if (!emailId) {
            return;
        }

        this.providerIdEmailIdMap[providerId] = emailId;
        return emailId;
    }
@private
@param {string} providerId
@returns {Promise<string|undefined>}