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Digital Literacy How the Internet Works The Internet TCP/IP

Posted by Patrick Masani
Patrick Masani
380 Points

What 'destination' address is stamped on the IP header of an email?

I'm curious, if I was to send an email to a friend. What would the destination be in the IP header? Obviously, the TCP/IP wouldn't know my friends actual IP address until he receives the email, correct? So then what IP address is considered the 'destination'? would it be the Email database? Also, what about using the same email address on multiple devices? Let's say you downloaded an email "attachment" on multiple/different devices. Are all the different IP addresses added onto the 'destination' list?

1 Answer

Steven Parker
Steven Parker
229,670 Points
Steven Parker
Steven Parker
229,670 Points

When a email message is sent, the software makes a DNS request using the domain part of the email address. The DNS system returns the IP address of the MX ("Mail eXchanger") that has been listed for that domain. That's the actual IP address that the message is sent to via TCP/IP. It will repeat this process for each address in the distribution list.

To receive email, the software on the other end contacts the same system to pick up messages being held there by the mail server.

Receiving a message, with or without downloading any attachments, does not affect the distribution list.