the process is little more complex than this explanationbut this is essentially what happens in factit' much the same as the process used when working with physical letters in that the essential steps are the same with physical mailthe -mail application is replaced by you on one end and the recipient at the other the smtp server is replaced by the post office and the employees who work there (including the postal carriershoweversomeone generates messagethe message is transferred to recipientand the recipient receives the message in both cases defining the parts of the envelope there is difference in how the envelope for an -mail is configured and how it' actually handled when you view the envelope for an -mailit looks just like letter in that it contains the address of the sender and the address of the recipient it may not look physically like an envelopebut the same components are there when you visualize physical envelopeyou see certain specificssuch as the sender' namestreet addresscitystateand zip code the same is true for the recipient these elements definein physical termswhere the postal carrier should deliver the letter or return the letter when it can' be delivered howeverwhen the smtp server processes the envelope for an -mailit must look at the specifics of the addresswhich is where the analogy of physical envelope used for mail starts to break down little an -mail address contains different information from physical address in summaryhere is what the -mail address containshostthe host is akin to the city and state used by physical mail envelope host address is the address used by the card that is physically connected to the internetand it handles all the traffic that the internet consumes or provides for this particular machine pc can use internet resources in lot of waysbut the host address for all these uses is the same portthe port is akin to the street address used by physical mail envelope it specifies which specific part of the system should receive the message for examplean smtp server used for outgoing messages normally relies on port howeverthe point-of-presence (pop server used for incoming -mail messages usually relies on port your browser typically uses port to communicate with websites howeversecure websites (those that use https as protocolrather than httprely on port instead you can see list of typical ports at en wikipedia org/wiki/list_of_tcp_and_udp_port_numbers