How to know if if the sent mail is

I think you meant to ask "How to know if the sent mail is delivered?"

Here are a few ways to check if an email has been delivered:

1. Read Receipt: You can request a read receipt from the recipient, which will send a notification to your email when they open the email. To do this, you'll need to enable read receipts in your email client or use a service like Sanebox.
2. Delivery Reports: Some email providers, like Gmail, offer delivery reports. These reports will show you if the email was delivered to the recipient's inbox or if it was bounced back due to an invalid email address or other issues.
3. Bounce Back: If the email is undeliverable, you may receive a bounce back message from the recipient's email server. This message will usually indicate why the email couldn't be delivered.
4. Follow-up: You can also send a follow-up email to the recipient to confirm if they received the original email.
5. Email Tracking: Some email clients, like Mailtrack or Yesware, offer email tracking features that allow you to see if the email was opened, forwarded, or replied to.
6. Check the Recipient's Response: If you're expecting a response from the recipient, you can wait for them to respond to your email. If you don't receive a response, you can try sending a follow-up email to confirm if they received your original email.

Keep in mind that there are no guarantees that an email will be delivered or read, as email delivery can be affected by various factors, such as spam filters, email client settings, and internet connectivity issues.