Now let us look at how a email is transfered form the sender to the reciever.Now this involves some protocal
which you may have to browse and look for the working of those protocal however i have tried to explain them too

Now the sender sends an Email and the Reciver recives it. How is this done ? The sender types the email in the
mail user agent . this is the outlook express in windows or ththunderbird in linux. But now all the well know
email servers has inbuilt mail user agent so that you need not use one seperately.

Now when the email is sent it reaches the mail server of the sender that is the senders mail server from the
mail user agent. This is done using the SMTP .

SMTP is simple mail transfer protocal and this is used in most of the mail transfers.

Now the mail has reached the senders mail server. From the senders mail server the mail is being transferred
to the recivers mail server and this is done again by using SMTP protocal

At this point dont be confused what is a protocal.Protocals are nothing but a set of Rules.

Now the mail has been recieved at the recivers mail server from the senders mail server.Now the work of the recivers
mail server is that to ensure delivery to the reciver mail user agent. This is done only when the reciver request
for the mail and then the mail is Given to the reciver.

This is done by using either of the two protocals

i) POP3
ii) IMAP

POP3 was used in older days and still some mail servers uses pop3 protocal and this is nothing but POST OFFICCE
PROTOCAL 3 and in this case the mail is actually transferrd from the recivers mail server to the recivers mail useragent

But the Drawback is that there is a possiblitty of a hacker to hack into this transfer.So modern mail servers like
GMAIL uses IMAP.

Here in IMAP the mail is not transferred between the mail server of the reciver and the mail user agent of the
reciver but just a connection is established between and the mail useragent reads directly from the server

This is how a mail is sent and recieved accross the internet.

And one more important point

Email works as a connection-less service. What this means is that when mail is transferred from sender to receiver no connection is established between the two parties. And so you never know whether your mail got delivered or not