help with smtp and imap explaination

help with smtp and imap explaination

Post by Hung Ngoc La » Tue, 02 Oct 2001 08:21:33



Hi Everyone,

I know that I have been posting a lot of questions the
last couple of days; however, I am just trying to learn
as much as I can with Unix especially Linux for the
past 10 months.  Coming from a Windows background,
I think Linux performs so much better than windows.

I've successfully setup a mail server for server for my
home network.  I registered for a domain (hnl.com)
from Network Solutions and my ISP assigned me a
static IP address 199.0.216.125.  I've asked my ISP
to host my domain name, namely:

www.hnl.com (199.0.216.125)
ftp.hnl.com (199.0.216.125)
mail.hnl.com (199.0.216.125)

I am running sendmail-8.11.2-14 on Redhat Linux 7.1
with kernel 2.4.9.  Furthermore, I am running sendmail
on the same box as my Firewall (bad idea, I know).
The firewall has the following address:

outside: 199.0.216.125
inside: 172.16.1.254

My private network is 172.16.1.0/24 and users on
this network have email account on the Linux mail
server in order to send/receive mail on the Internet.
Oh by the way, users send/receive mail via Microsoft
Outlook/Outlook Express.  As I've said before,
everything works; however, I don't want to be a
dummy.  I would like to understand the fundamental
aspect of mail server.

Here are my questions:
1)  How many components are there in the Mail
    Server?  Is it true that for users to send mail to  
    other users on the Internet, SMTP (port 25) must
    be running on the mail server.  Is it also true that
    SMTP is used to transport mail between
    mail server?

2)  In order or users on my private network to
    receive mail from other users on the Internet,
    I have to install a package called imap
    (imap-2000-9) on the same system that I install
    sendmail.  From what I understand, imap, provides
    services such as POP3 and IMAP2 so that users
    on my network can retrieve mail.  What is the
    associations between IMAP/POP and SMTP?

3) Is it possible for me to run SMTP and IMAP on
   separate Linux machines?  I would like to move
   the mail server to another machine behind the
   linux firewall.  I am going to get another static
   IP address from my ISP and I will use Network
   Address Translation (NAT) to NATed the mail
   server to the Internet.  What service will I have
   advertise to the Internet, SMTP or IMAP? If I run
   IMAP and SMTP on different machines, how will
   mail from the Internet know how to get to my
   network? I am really confused about this part.

4) I think I understand what "mail-relay" means.
    I even modify the /etc/mail/relay-domains file
    to allow only users from my private network
    to use smtp to send mail (prevent spamming).
   Am I correct with the definition of "mail-relay"?

5) Go back to question 3, if I replace the machine
   that runs IMAP with a Microsoft Exchange Server,
   is the same thing still applied?

I know some of the questions might sound obvious
to some people, but I have trouble understand the
concept.  I've been reading a lot of books from
O'reily on this topic but the more I read about it,
the more I am confused about it.  Please help me.

Many thanks.
David

 
 
 

help with smtp and imap explaination

Post by Petr Klyushki » Wed, 03 Oct 2001 02:49:31


Hello, Hung!

Quote:>>>>> "Hung" == Hung Ngoc Lai writes:

 Hung> Here are my questions: 1) How many components are there in the
 Hung> Mail Server?  Is it true that for users to send mail to other
 Hung> users on the Internet, SMTP (port 25) must be running on the
 Hung> mail server.  Is it also true that SMTP is used to transport
 Hung> mail between mail server?

AFAIK, yes.

 Hung> What is the associations between IMAP/POP and SMTP?

Mail is sent (by users2servers or servers2servers) with SMTP. Users
fetch mail with IMAP or POP.

 Hung> 3) Is it possible for me to run SMTP and IMAP on separate Linux
 Hung> machines?

Dunno, never tried to do this.

 Hung> 4) I think I understand what "mail-relay" means.  I even modify
 Hung> the /etc/mail/relay-domains file to allow only users from my
 Hung> private network to use smtp to send mail (prevent spamming).
 Hung> Am I correct with the definition of "mail-relay"?

AFAIK, yes

 Hung> 5) Go back to question 3, if I replace the machine that runs
 Hung> IMAP with a Microsoft Exchange Server, is the same thing still
 Hung> applied?

See my answer on q3 :-)

--
                                                             C'ya, Peter.