Clients connect to the mail server to send and receive mail using an SMTP-compatible mail client, such as Claris Emailer, or Eudora, or Microsoft Outlook Express.
Person addresses envelope with the recipients PO box and zip code.
Person brings the letter to his local Post Office for delivery. If the mail is being sent to a user who has an account on the same server, the mail is placed in his mail folder, waiting for the client to connect to receive it. If the mail is being sent to that same zip code, the letter is put into addressee's PO box till he comes to get it. If the mail is addressed to another mail server, the mail server makes a connection to that mail server to deliver the mail there. If the mail has a different zip code, the piece of mail is delivered to that Post Office, where it is placed in the addressee's PO box till he picks it up.