putting it through the office franking machine was probably a mistake.
Quite, one should always ensure the bird's head is at the other end of the envelope, i.e. the top left above the recipient address and also quickly switch off the power (or quickly press the 'Bird Consignment' button on later models) before the whole packet goes between the rollers and into the mail out sack. The problem is, it's all to easy to fall fowl of the regulations if a sender just wings it.