How email system works

  •  A user u1 opens outlook and accesses mail host abc.com.
    • That mail host can be a Linux system running some mail server daemon e.g. postfix.
    • On that host, multiple users are created. 
  • User u1 from outlook logs in as a user at abc.com.
    • User writes a mail and send it to u5@xyz.com.
  • The mail first goes to mail server for domain abc.com.
  • abc.com sends it to mail server for xyz.com
  • The user u5 can access the host for domain xyz.com and read the mail.
  • on Mail client e.g. outlook a MUA(Mail user agent) runs, with which user writes and sends mails.
  • MTA (Mail Transfer Agent) i.e mail server transports the messages over internet.
  • Why we have used Agents?
    • Each type of operation is done through some agent(program).
  • Mail server runs a POP or IMAP server to hold users' mails.
  • SMTP(Simple Mail Transfer Protocol) is used to transfer mails.


Notes and doubts

  • Outlook == mail client = mail user agent
    • mail
    • Elm
    • Outlook
  • MTA == mail server, which uses SMTP
    • postfix
    • sendmail
    • Courier
  • Host == mail domain == A Mail server services a domain
  • There can be a mail exchange server for the domain.
  • User1 on Host abc.com ==> u1@abc.com
  • User5 on Host xyz.com ==> u5@xyz.com    
  • We can configure mail server on a linux machine. And without login, we can send and receive mails.



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