When I ask for an acknowledgment, the recipient does not receive anything (he does not receive the request for receipt), why?

He receives the email, but you do not receive a "Read Receipt" and the recipient is not prompted to send you one (Yes/No)?

Not all mail readers support read receipts, or they may have a setting to never send them. It simply is not an accurate way to determine whether the message was read.

That said, to see whether it is the mail reader or the mail sender, can you send a message with a request for a read receipt from webmail-to-webmail and see whether that works?

Hi,

Yes, he receives the email but the recipient is not prompted to send you one and of course I don't get anything.

I tested on 3 different recipients each with their own webmail. With Windows Live Mail, it worked with these 3 recipients.

I want to test by sending you an email, what is your email please?

devilsgatedrive at gmail.

sorry Matt, I do not understand

The email address was written phonetically - as you would speak it out loud - because it means spam bots will not detect it as a written email address. So when Matt says at he means the sign @ and gmail is followed by dot com as standard, where dot means a full stop/period punctuation mark.