How to know a mail is read in gmail

In Gmail, there are a few ways to determine if an email has been read:

1. Read Receipt: You can request a read receipt from the sender by adding the following text to the email body: ?readreceipt=1. This will send a notification to the sender when you open the email. However, this feature is not enabled by default, and the recipient needs to have it enabled in their account settings.
2. Email Headers: You can check the email headers to see if the email has been opened. When an email is opened, Gmail adds a header called X-Gmail-Read with a value of true. You can view the email headers by clicking on the three vertical dots next to the reply button and selecting "Show original".
3. Gmail's "Read" Indicator: Gmail displays a small blue dot next to the sender's name in the inbox if the email has been read. This indicator is only visible if you have the "Show read receipts" option enabled in your account settings.
4. Email Tracking: Some email clients, including Gmail, use email tracking to monitor when an email is opened. This is done by embedding a small image in the email that is loaded when the email is opened. The image is then tracked to see if it has been loaded. You can check the email's HTML source code to see if this image is present.
5. Third-Party Extensions: There are several third-party browser extensions and add-ons available that can track when an email is opened in Gmail. These extensions can provide more detailed information about when the email was opened, such as the time and date.

It's worth noting that while these methods can provide some indication that an email has been read, they are not foolproof and can be bypassed by the recipient.