3 ms·

nope, not sure about the gmail proxy servers but you get alerts everytime user opens the mail. speaking from first hand experience.

• pirsquare 6y ago
  That happens if email is opened via clients like Thunderbird. For gmail, image will be served via google proxy servers.
  • pixl97 6y ago
    What is the cache time for said proxy servers? Does it follow content expiration rules?
  • sroussey 6y ago
    In my tests using Gmail website, I see the read receipts right away.
    • bigiain 6y ago
      Do you see them the second or third time you open the mail?