to get an idea about how multiple protocols work on the internet to enable certain internet services a fun example is to talk about mail email is something you guys use all the time something you're very familiar with but how does email actually work so the story of how email is transmitted across the internet is pretty interesting and it also gives us a chance to talk about a couple of different protocols so let's um go back to this uh burining friendship between Greg and ziz so Greg has downloaded some of Z's pictures off her website um this is my cat by the way this is supposed to be a cat um Greg says it looks like a loaf um so Greg has has admired s's pictures on her website now he wants to uh he's emailed her and said oh those are cool pictures do you have any more pictures and of course this has lots of pictures particularly of her her doing things she's not supposed to be doing um and so she says okay I'm going to I'm going to send Greg uh an email so how does this actually work so the first thing to to to think to recognize with email is that email requires communication with some sort of email server um if you if you receive email at a particular email address for example let's say that Greg is using his uh Greg hotmail.com ziz is uh using her ziz gmail.com these names identify the mail server so this uh gmail.com it has to have a mail server that ziz can connect to to retreat for mail and Greg and hotmail.com has to provide a a email server that Greg can connect to and sometimes you access these uh using a web browser but the the process is basically the same so the first thing that happens when ziz sends an email is that there's an interaction between her computer and this gmail.com mail server so that mail server is located somewhere on the internet and the first thing that happens is that Z's computer has to tell Gmail that it wants to initiate a mail transfer uh a mail message to Greg hotmail.com so that's the first thing that happens and what's and and what's interesting to note is that this is not transmitting the mail this is just telling a mail server that I want the mail to be transmitted so this part of the interaction there are a number of different protoc calls that are used here um you may have heard of some of them if you had to configure a mail client uh one of them is called IMAP it's the internet uh mail access protocol um another one an older version is called pop which is not only a funny name for soda but uh stands for the Post Office protocol um there's also exchange protocols that Microsoft has developed that work here but these Protocols are designed to allow a male client to communicate with a male server to do do things like Retrieve mail send mail organize mail Put mail into folders things like this so this uh these Protocols are uh protocols that run between a male client that typically runs on your computer and a male server that you connect to that's the first step in send a mail but when uh Z's computer successfully tells Gmail that she wants to initiate a message transfer the message actually hasn't reached Greg's mail server yet so what Gmail will do is Gmail uses another protocol this is called SMTP so SMTP stands for these simple mail transfer protocol and the simple male transfer protocol is what mail servers use to communicate with each other so once ziz tells Gmail's mail server I want to send mail to Greg hotmail.com Gmail will start the process of transmitting that message across the internet using the simple mail transfer protocol to the mail server run by hotmail.com and this may involve several uh attempts you might have seen uh messages from the SMTP protocol saying that your mail was delayed or wasn't able to be delivered for example the SFTP protocol allows hot mail to say um you must have have a wrong that you must have fat fingered the username because there's no user uh called you know Greg the catlover at hotmail.com um and so the smt protocol allows servers to communicate about sending mail about um rejecting if they don't know who the recipient is things like this so this is the core protocol that male servers use to communicate with each other once the mail arrives on at Hotmail uh hotmail's email server then there's this extra interaction between Greg's maale client or computer and the server itself and this is another part of these protocols IMAP and POP and protocols like this they not only have to be able to allow you to send mail but obviously you need to be able to retrieve mail so periodically uh Greg's computer will communicate with the mail server at hotmail.com and it may say Hey you have this new message from ziz gmail.com um and that includes some some really cool new pictures of herself so so this is a you know a great example it's a little complicated but this is an example of how multiple protocols on the internet work together to do one very simple thing allow you to send email oh