Email Flow

Email- Electronic mail is one of the best way to communicate for computer users anywhere in the world. If i wanted to write an email message to my friend who is sitting somewhere in the world, i simply open up my outlook-click on compose-type my friends email address in the to box-mention the subject-draft the message-attach files(if needed)-click on send.That's it. This is what i do to send an email to my friends.Not only me, all the computer users will do the exact same thing.But for most of the time i didn't know how the mail flow takes place.How the transfer takes place and how will it reach the recipient and the intermediate process and so on....
In this post i am presenting you the basic scenario of the mail flow which i learned in the recent days. Hope you will find a bit use full
There are a few new keywords we need to look into......
1. MUA - Mail User Agent. MUA is the email client which we use to create-draft-send emails. Generally Microsoft Outlook, Thunderbird,Kmail and so on....... are examples of MUA's

2.MTA - Mail Transfer Agent. Message.Mail transfers between sender(s) and recipient(s) will take place between the MTA's. Exchange, Qmail, Sendmail, PostFix and so on.... are example of MTA's

3.SMTP : Simple Mail Transfer Protocol will transfer the mails between the MTA's

Lets take a deeper look into this with a small example. The below picture will depict how mail flow takes place between sender and recipient

From the above picture, When the sender clicks on Send in his MUA, the mail will be transferred to the MTA of the sender which exists in the Mail server of the Sender. The MTA of the sender will check for the recipients address( MX records-Mail Exchange Records) and if it finds the recipients address then the mail will be flowed from Senders MTA to Recipient MTA using the SMTP Via TCP Port 25. Once the Recipients MTA receives the email, it will be transferred to MUA of recipient. Once the Recipient Clicks on the Send/Receive button then the email will be once click away from him residing in his inbox.

In addition to the above processes there is another agent called as MDA-Mail delivery agent. MDA will receive the email from the MTA and will deliver it the the recipients MUA.