How to know if a mail has been read 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 on their end as well.
2. Email Headers: You can check the email headers to see if the email has been opened. When you open an email, 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 Gmail settings.
4. Email Content: Some email clients, including Gmail, may include a "read" indicator in the email content itself. For example, some emails may include a line like "This email was opened on [date] at [time]".
5. Gmail's "Open Tracking": Gmail has a feature called "Open tracking" that allows you to see when an email has been opened. To enable this feature, go to your Gmail settings, click on the "General" tab, and scroll down to the "Open tracking" section. You can then toggle the switch to enable or disable this feature.

Keep in mind that these methods may not always work, as some email clients or services may not support read receipts or may have their own ways of tracking email opens.