Your user account page on the Sidekick site shows your tracked emails listed as an "activity stream." Basically, these are the same cards that appear when you click the Sidekick icon button.
Interestingly, if you open your own sent email that you're tracking through Sidekick, you'll receive a notification for that as well. This actually has a useful purpose -- it is meant to alert you if someone may be accessing your personal account on Gmail and opening tracked emails in your Sent folder without your knowledge.
Sidekick can track link-clicks, but only if the links are set as hyperlinks in the text of your email -- unlike with most of the other services in this roundup, you can't just enter an URL (for example: www.computerworld.com) into the body of text. Once you've embedded the link, Sidekick will track the number of clicks to that link.
Free and paid plans
Free accounts are granted 200 notifications (for whenever a tracked mail is opened) per month. For $10 per month, the 200-notification limit is removed.
Compared to the other extensions in this roundup, Sidekick's extension modifies the original user interface of Gmail the least -- the only new element it adds to the email composition window is the aforementioned checkbox for activating tracking.
I liked the design of Sidekick's notification cards, and how you can use them to keep up with the status of your tracked emails without needing to visit your account page. In addition, the limit of 200 notifications means that most users will be able to keep to the free account, while business users can handle the reasonable $10 per month fee.
Yesware is geared toward the business user, as evidenced by its (for pay) reporting features for CRM and Salesforce accounts and its add-on for Outlook.
How it works
The Yesware extension inserts its own toolbar into Gmail's composition window; the toolbar includes a checkbox that lets you turn tracking on or off.
It adds another toolbar, called the Inbox Dashboard, to the main Gmail screen, above where your emails are listed. An Events button makes the toolbar expand down to show a list of when tracked emails have been opened and lets you turn off tracking if you wish. An Emails button shows you all the tracked emails you've sent and whether the recipient has opened an email, clicked a link inside it, or replied.
The Inbox Dashboard isn't integrated seamlessly; it operates like a separate utility that's laid over the original Gmail UI. In my testing, this toolbar took a couple of seconds to load after the main Gmail screen was fully loaded. You can switch off the Inbox Dashboard, but you then have to visit your account page on the Yesware site to follow the tracking statuses of your emails.
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