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Some people and companies embed hyperlinked images in their emails in order to keep track of which recipients read the emails, and when. When the recipient opens the email and their email client asks the server for the embedded image, the sender gets a log of that. Usually, the URL to the image is unique, that way the image server can tell exactly which email just got opened. However, in many cases the URL is not unique. I have seen the following line in several emails from at least two senders:
<img class="" src="https://mail.google.com/mail/u/0/images/cleardot.gif">
I have unencoded the string above into plain HTML. In the email, it is usually in quoted-printable format, so the = characters turn into =3D.
How does this hyperlinked image track recipients? It can obviously get your IP address and the time you opened it, but that doesn't seem very helpful. I don't understand why anyone would include this image without a unique URL.
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There is also a discussion on the Gmail Help Forum: https://productforums.google.com/forum/#%21topic/gmail/dEgRYxLWDjA There a Google representative claims that the image is being used just as a spacer.
– pabouk – 2016-12-09T09:03:47.513A 1x1 spacer. Only for the eagle-sighted among us, or the very gullible. – None – 2019-05-06T21:17:34.203
1Another reason to always read email in plain-text only. – Synetech – 2013-10-15T14:18:52.297