Why do we need to use SMTP when the receiving server doesnt use the same protocol to read the messages?
Based on my understanding, when a computer sends an email, the application layer sends it down to the transport layer via the SMTP protocol and this is how the TCP segment would look like - Source Port : (some ephemeral port), Destination Port - 25 (SMTP port), Data.
The destination port is included here because when the receiving computer receives the segment, it should know what application layer protocol it needs to send the data to.
But as far as I know, the emails are retrieved and read using POP/IMAP protocol.
So what is the point of even including the SMTP port number here and how is this interpreted on the application layer on the receiving computer?
