And every month he mailed a postal money order.

每个月他都会寄一。

He's most likely in jail for stealing a postal order.

他有可能因为偷了一而坐牢。

There were a dozen of them hell-bent on stealing postal orders.

当时可是有一大群人拼命想偷走呢 是指付给某人一定金额的凭据。