[H-GEN] Basic pop3 server

[Robert Brockway]

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On Tue, 13 May 2003, Stuart Longland wrote:

> Okay, you'll also need SMTP for this (to send email, POP3 only receives
> it).  We're using QMail here, and so far, I've found that reasonably
> reliable and simple to set up.
>
> Others may recommend Postfix (we had no luck there), Sendmail (very old
> but very well known) and Exim (don't know anything about this one), but
> basically, it's a case of whatever works for you.

The "Big 4" unix MTAs (mail transport agents) are all under active
development.

These are sendmail, exim, postfix and qmail.

Which is best is a matter of religious debate.  I've had the opportunity
to play with all of these except postfix to varying degrees.  I'll be
giving postfix a try shortly.

Here are a few thoughts.  I hope to be as objective as possible.

Sendmail)

Sendmail is by far the oldest of the Big 4.  Afaik it is infact the oldest
unix MTA and is definately the oldest still being actively developed.
Sendmail has had a bad reputation for security problems in the past.  The
sendmail developers put a lot of time into securing sendmail and the only
exploits it has had in recent years were two very obscure long standing
ones that were discovered and cleaned up recently.  They had been there
for years and been missed by all the hax0rs.  These exploits were
discovered by an extensive security audit.

Sendmail also has a reputation for being hard to configure.  This is
really undeserved.  Everyone configures sendmail through m4.  A macro file
is written (might be 12-20 lines long, based on a template) and the config
file is then generated.

Because of its age there are far more sendmail gurus around than for the
other MTAs.  This has value from a business PoV as it is possible to pull
in contractors from many sources who can work on sendmail.  Almost all
unix mail admins have had some exposure to sendmail.

Similarly, there has been a lot written about sendmail.

Exim)

A newer MTA designed to be easier to manage than sendmail.  The config
files are readable without having to have a great understanding of what
the MTA is doing internally.  Not a bad MTA at all.  My exposure to this
MTA has been solely through the Humbug mail server caliburn.  I've found
Exim too keen to "freeze" items in the mail queue, requiring human
intervention to get them out (some of them never leave).  Perhaps this is
configurable but I haven't seen much on it (admittedly I haven't delved
too deeply).

Qmail)

Written by the mathematician Dan Bernstein (DJB).  DJB is the author of
DJBDNS of course.  There has never been an remote root exploit in qmail as
supplied by DJB.  He has actually offered a cash reward to anyone who can
find a remote root exploit in the pristine qmail code.  The prize remains
unclaimed.

I have found qmail a little too keen to bounce mail out of the queue.  I
had a situation recently where my backup MX (running qmail) bounced a mail
item addressed to me with a permanent failure.  There was no good reason
for this to have occured.  The qmail box should hold my mail for 7 days,
this occured almost as soon as it got the mail item.  I have 6 dns servers
for my personal domain, so it should have been able to contact one of
them, and besides if it can't contact any it should defer mail delivery
and attempt redelivery later.  I am still at a loss to explain the mail
bounce.

I also know of a situation where there was a misconfiguration in the dns
for a domain.  The primary MX did not resolve.  Qmails's solution (again
as a backup MX) was to elevate itself to the primary MX, and then,
deciding that it could not delivery the mail locally, bounce all the
mail items with a permanent failure.  Elevating itself to the primary MX
was a mistake.  Sendmail holds the mail with a transient failure in the
same situation.

Having seen these two situations recently I am now more wary of qmail as a
backup MX.  I'm sure it functions well as a primary MX.

Postfix)

No idea :)

Rob

-- 
Robert Brockway B.Sc. email: robert at timetraveller.org  ICQ: 104781119
Linux counter project ID #16440 (http://counter.li.org)
"The earth is but one country and mankind its citizens" -Baha'u'llah

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