postfix

[Ben Scott]

On 8/29/07, Paul Lussier <p.lussier at comcast.net> wrote:
> Or /bin/mail...  Technically it is the LDA which does the
> user-existence verification checks, not the MDA.

  An LDA is a type of MDA.  Any LDA is also an MDA.

  If you meant "MTA", then again, I point out that an MTA can also
perform address verification, and Sendmail does this "by default" (as
much as any Sendmail behavior can be called a "default" <grin>).  If
you don't believe me, connect to TCP/25 on liberty.gnhlug.org and try
RCPT TO:<nosuchuser at gnhlug.org>.  It will reject it then and there,
before any MDA is invoked.

  This *is* rather esoteric, but you keep bringing it up...  ;-)

> If Exchange does this, it's because someone thought to build an AD
> query into the interface that does so.

  There's no default "all users" DL (Distribution List) in any part of
AD, Exchange, or Outlook.  Kind of surprising, really.  Microsoft
likes that kind of thing.

  One can mail-enable the "Domain Users" group or similar.  And one
can, of course, create any number of manually-maintained DLs.  The
same goes for Sendmail -- I've maintained "everybody" aliases before.
Of course, in these days of spam, you would need some kind of access
control on such.

>> POP and IMAP servers would probably be considered MUAs (Mail User
>> Agents) as far as the standards are concerned, since they're all about
>> accessing user mailboxes.
>
> I wouldn't consider POP or IMAP an MUA.

  *I* wouldn't either.  But as far as I know, as far as the RFCs are
concerned, there are MTAs (which move mail around), MDAs (which accept
and process mail for delivery), and MUAs (which handle mail on behalf
of the user).  Oh, and MSAs (Message Submission Agent), which is a
subset of SMTP for MUAs that only inject mail.

> POP and IMAP simply store it until picked up by the authenticated user.

  IMAP typically stores it afterwards, too -- unless your initials are
"pll".  ;-)

> Perhaps 'Mail Storage Agent' ?

  I like it, but it collides with MSA.  Maybe "Mail Box Agent"?  Then
all us sysadmins can claim we've got an MBA.... ;-)

>> Exchange itself will never be an MDA for a Sendmail or Postfix ...
>
> Never say never.  Let's all agree that we *hope* we never need to use
> Exchange as an MDA for a postfix or sendmail system!

  Well, I suppose if you had Sendmail or Postfix running on a Exchange
server, and you also wrote a custom MAPI or CDO program to inject mail
into the Exchange Information Store without using the Exchange SMTP
service, then you could do that.

  But otherwise, you're just going to be using the SMTP relay function
as the MDA for Sendmail/Postfix.  (In Sendmail, this is the "smtp"
mailer.)

> In fact, we discovered the theoretical possibility of a mail message doing
> figure-8s between our sendmail/cyrus server and the Exchange server!

  I used to work at UNH.  Imagine hundreds of computers, used by
faculty/staff, running anything from DOS to MacOS to NetWare to doze
to nix.  Many of them processing mail for their primary user.
Sometimes mail hopped between four or five systems before end-user
delivery.  One scenario I saw was first.last at unh.edu ->
username at cismachine.unh.edu -> username at dept.unh.edu ->
username at oldpersonalmachine.dept.unh.edu ->
username at newpersonalmachine.dept.unh.edu!  You can imagine what mail
loops were like in that environment...

>> One of the reasons I like Linux so much is that everything is
>> included "in the box"; I don't need to buy eighteen more tools for
>> every server.
>
> Exchange lovers say much the same thing :)

  No competent Exchange admin I ever met would run without at least
some anti-virus software.  Most also recommend third-party backup and
mail filtering add-on tools.  And there's no end of further add-ons
(faxing, disclaimers, archiving, compliance, management, monitoring,
etc, etc.).

  I'm sure there are PHBs who say that about Exchange, because they are PHBs.

http://www.dilbert.com/comics/dilbert/archive/dilbert-20070803.html

>> Even ignoring that, Active Directory and MS-DNS are part of Windows
>> (a separate product, purchase, and license), not Exchange.  And the
>> SMTP ideas of "MTA", "MDA", and "MUA" don't really apply to Exchange.
>
> Maybe not, however, it's rare that you'll find a shop running Exchange
> which does not also run MS-DNS and AD.  They may well be add-on
> products, and you may well have to buy them, but from what I've seen,
> people who run Exchange just accept that and go ahead.

  Well, sure.  But your assertion was that it's all one product, and
it ain't.  :)

>  Basically, once the SMTP service receives the mail into Exchange
>  all bets are off!

  I regard myself as a competent (albeit reluctant) Exchange admin, so
I'll have to disagree.

-- Ben