Those of us who have used email alot, (see my email memories story here) have often wished we could know if our recipients have opened and read our messages. And while there have been read-receipts on various email services for many years, until now there hasn't been a general-purpose tool that can track when someone actually opens your messages. Enter Zendio with their plug-in for Outlook. And while it works, it is probably the creepiest solution that I've seen.

For Zendio to work, all your messages have to originate from your Outlook inbox, which makes sense. You install the plug-in, which is somewhat of a misnomer because it requires all sorts of Microsoft support software, depending on which Windows OS and which Office version you are running. I tried it on XP with SP2 on Outlook 2007 connecting to my Google Apps mailbox and it seemed to do fine. It embeds small snippets of HTML code into your messages to enable the tracking feature.

Zendio shows you exactly when someone opened your message, and tries to geolocate the recipient. It wasn't completely accurate for my simple test, although it did come within a few miles of where I was, as you can see here:

You can also include trackable links or other objects in your message, similar to how ConstantContact and other email campaign managers work. If someone clicks on the link, you get a report showing you the details. You can also see a summary report of the behavior pattern of the particular times of day that someone is using their email client, and how long it takes from when you send something to when it is actually read. That is what got my creepiness meter moving up.

Zendio includes the ability to make pretty signatures and email stationery, but it also appends (for the free trial) its own annoying trailer to each of your emails. All of the messages are sent via your own email server.

Outlook has its own read receipts that only work when your recipients are using Outlook themselves, and most other products generally request that you acknowledge the read receipt when you open the message. Zendio removes these restrictions.

The service is $10 a month per user. There is a 30 day free trial available. You need to be running Outlook 2003 or later on XP or later Windows machines. Outlook 2010 is only supported on 32-bit OS.