 | | | sendmail configuration on redhat | sendmail configuration on redhat 2003-01-17 - By David Freeman
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> For my own clarification , is there a difference between
> Handling POP3 and SMTP requests , and actually BEING a POP3 / SMTP
server ?
I guess that depends on what question you think you're asking.
SMTP = simple mail transfer protocol (from memory, it's a while since I
actually checked that - could be simple mail transport protocol).
An SMTP server runs on port 25 and handles sending of email as well as
receiving email from clients to be delivered (either locally or to some
SMTP server on the net somewhere).
POP3 = post office protocol
A POP3 server runs on port 110 and handles incoming requests for mail
delivery from a client program.
As both protocols work on different ports they quite happily co-exist on
a single machine. It's no different to running a web server and DNS
server on the same computer. The only thing you can't really do is run
two daemons that want to use the same port and IP address combination.
That said, on Redhat systems, the SMTP daemon is usually sendmail. This
is NOT a POP3 server. You will also find a POP3 daemon - the newer
releases are incorporated into the IMAP rpm from memory.
As for the question, if you're "handling" POP3/SMTP requests then you're
most likely operating POP3/SMTP daemons. You could, however, be
proxying such requests which could be said to be "handling" without
being a "server" depending on your definition of those terms.
Every RH release I've used (seriously from about RH5, earlier as a hobby
thing and I don't really recall for those earlier releases) is readily
capable of acting as a mail server (both POP3 and SMTP) with no real
requirement for altering sendmail.cf although before relaying and the
like became common it used to be necessary to generate your own
sendmail.cf if you wanted that sort of functionality. Most recent
releases have had this capability ready to run.
Perhaps if the person having problems cannot get mail serving working it
could be related to DNS and, particularly, MX records rather than
configuration of the daemons themselves.
> If sendmail is
> not
> a POP server , how does it handle the incoming mail ?
Incoming mail is the job of a mail transport agent, or MTA (a program
that moves mail between servers). The usual protocol is SMTP and this
is what sendmail does.
Delivery of mail to a client (Outlook Express et al) is the job of a
mail delivery agent, or MDA (a program that waits for client connections
and sends locally stored email to that client). The usual protocol is
POP3, although IMAP is also now popular, and this job is handled by a
POP3 daemon (these days part of the IMAP rpm).
CYA, Dave
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