Whatever format you choose, I'd like to suggest that you include a small bit of identifying info at the beginning of the number. For example, if your company na

Whatever format you choose, I'd like to suggest that you include a small bit of identifying info at the beginning of the number. For example, if your company name is Fictitious Enterprises, your confirmation numbers will always begin with "fe", as in fe7623. Or, have the confirmation numbers always begin with, say, "88", as in 887623. This tiny piece of redundancy is tremendously helpful for customer support staff and for your programs to recognize that a customer is giving the wrong number. In web forms, you can also prompt people to enter the number beginning with "fe" or "88". It's not the norm, but there's plenty of precedent for putting in a redundant prefix like this. And for heaven's sake, keep the number to a reasonable length, and if longer than 6 digits, break it up with hyphens, and make sure that all your web forms accept the number with or without the hyphens if copied & pasted. I've seen confirmation numbers, order numbers, etc., that run to absurd 30 or 60 or more digits, enough to encode all the protons on Earth. There are always cases when you can't copy & paste (like from screenshots, paper printouts, one device to another, spoken over the phone), so you don't want crazy lengths.