SUMMARY: what is POP3 and what is mailhost and relay host

From: Alessandro Coppelli (
Date: Thu Aug 24 1995 - 04:39:45 CDT

Hi to all.

This is the summary of some of my questions.
I hope helping someone and I hope also my English is almost apprehensible.

I question :
What's POP3 ?

POP3 is a program that allows PC and MAC machines to read the mail that is
arrived to the mailserver machine.
When you can find the program: ( that is called popper or qpopper ) /support/pub/unix /quest/unix/servers/popper
What you must do after taking program

1) put it in a directory example /usr/local/bin
2) edit the file /etc/inetd.conf and add the following line

     pop3 stream tcp nowait root /usr/local/lib/popper popper -s

3) edit the file /etc/services and add the following line
     pop3 110/tcp # Post Office Protocol

The end !

I question

Definitions of mailhost relay host

Mailhost is the machine that inside of my local net ( or zone ) distributes the mail knowing exactly
where the mailserver of the single client is, allowing every one , in the world ,to send a mail by
simply writing an address whitout knowing who the mailserver is.

   ( and no -- sun3 is my mailserver )

What relay host is ?

Relay host is the one who able to speak, or better to translate all different formats for sending a
mail between unix machine, unix and PC machine ecc. ecc.
That is relay host or better major relay host.

Now, how can I say to all in the world which my mailhost is ?
Thank of DNS.
You must write on the principal server of your zone, in the zone file, in your local net is the
mailhost machine.


How the setting for the relay host and the mailhost can be made ?

In the RR SOA ( the file of zone in /var/named/ ) you could find some thing like thus :

  IN MX 10
  IN MX 20 name of relay host

( First sun1 -10- then relay host -20- .... )
( For setting you look in mail manual Sun How to set up a mailserver,mailhost,relay host )

Hoping to have been clear. I thank all ones ( and they are a lot of persons ) that have answered to my

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