Can an email attachment be configured to, in some way, notify the sender upon opening and other details?

I do not necessarily mean in a malicious way, but can normal-looking attachments like PDFs have some kind of hidden function to let the sender know information about the recipient, specifically, attachments received in Gmail?

  • That's going to depend on the nature of the attachment. It really has nothing to do with Gmail; Gmail is simply the delivery mechanism. If you are concerned about the security of the PDF format, perhaps Information Security would be a better place for your question.
    – ale
    Apr 23, 2015 at 12:48
  • It is not the attachment instead it should the file which is affected by unknown programs.
    – BDRSuite
    Apr 23, 2015 at 15:26
  • Ok thanks I just asked because I thought Gmail was great at auto-scanning unwanted programs?
    – Seeder
    Apr 25, 2015 at 18:22

1 Answer 1


In short, yes, this is entirely possible.

Many types of files can have metadata set to notify the sender when the attachment is opened. Since this usually isn't seen as malicious, Gmail's attachment scanning is not likely to flag it.

  • Is there a way to know which emails contain that kind of stuff?
    – Seeder
    Apr 23, 2015 at 7:49
  • For attachment file, you will be able to find them with a good antivirus.
    – John Hill
    Apr 23, 2015 at 12:08
  • For attachment file, you will be able to find them with a good antivirus. For link to images, just look if there are external link in the email and if there is an id instead of a direct link. Ex: mysite.com/img/image1.jpg is ok and mysite.com/img/image1.jpg?id=123456 will certainly inform the server that you have open the email. If it is present in the attachment (HTML page as example), it will do the job as well. Most email for advertisement contain this kind of stuff to know if you have open the email or not.
    – John Hill
    Apr 23, 2015 at 12:15

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