Sometimes when sending an email to someone, I need the recipient to inform me once he receives the email. There are the following words that I might use, but I don't really know whether they are correct or not:
1. Please aknowledge your receipt.
2. When you reveice this email, please let me know.
3. Please let me know once you receive this email.
4. Please reply with a "well-received", so that I know that you've received.
Which one is natural? Thanks a lot!