How do Gmail and the likes check if email is delivered
How do Gmail and the likes check if email is delivered?
Gmail doesn’t check. It can’t check. All Gmail ever has found out is if it successfully paid a contact communication to a server that responded at an address that is listed (in the web site NAME System, via an MX record) to be in charge of delivery to addresses in a recipient’s website. It generally does not know if the communication was supplied. For all those Gmail knows, the getting server’s incoming data was hijacked by criminals who stole the e-mail rather than delivered it. For all those Gmail has learned, the communication was received by the right server, but malfunctioning software on that server decided that the communication was junk and immediately erased it - without delivering it to anyone, without conserving it in any way, and without sending back a failure notification.