I’m sure for some “email appending” is just a pretty name for buying email addresses; some sort of legal loophole morally justified because, well, they’ve bought stuff from you before, but just never got around to subscribing to your promotional messages…. 

It doesn’t matter if your sales records show that Betty Smith spends $1,000 every other week on your Web site or your retail location.  It doesn’t matter that she’s on a first name basis with any of your staff, remembers your kid’s birthdays, sends you a fruit basket on your anniversary, or plays canasta at your house on Thursday nights; Betty didn’t give you permission to send her promotional email messages.

The value of email appending doesn’t come from adding email addresses to data that you have, it comes from adding data to email addresses that you have.

Let’s be realistic; if someone is buying from you online you already have their email address.  And if someone is regularly buying from you offline, what real value comes in having an address of someone that didn’t freely give it but buys from you regularly?

On the other hand, if I have a list of let’s say 1,000 opt-in email addresses, and I can append user data to those addresses I might find find that 68% belong to women. 

If I know from my own benchmarks that when I segment by gender I see a 10% increase in conversions, appending gender data to email addresses might make sense.  It doesn’t matter what the data points are – well, except to your organization, and all – the idea is still the same.

You might want to think twice about adding personalization to messages to people that didn’t provide you with that information.  It will probably come off as stalkerish-creepy and maybe bring a different result than hoped for.

I’m all for appending email addresses with additional data if it helps to send relevant and timely messages to subscribers, but appending email addresses that you don’t have to data that you do is, in my opinion, just a fancy way of buying email lists….