postfix

[Ben Scott]

On 8/27/07, Paul Lussier <p.lussier at comcast.net> wrote:
> There is no easy way to do this if you're simply using postfix to
> relay mail between many mail servers within your domain.

  This is perfectly true.  But a lot of people running a "mail server"
just have one server, with final delivery at that mail server.  I was
ass-uming that's what the OP meant in my own post, and never even
considered the mutli-server possibility.  Good point!  But for the OP,
ass-uming my ass-umption was correct, all those relaying/MDA concerns
evaporate.

> Postfix is simply an MTA, as such, it does usually validate the existance of a
> mailbox for a given piece of e-mail (sendmail doesn't do this either).

  If you're doing local delivery, validation is indeed the default
behavior prior to delivery.  At least, it is for Sendmail; I can't
imagine Postfix is any different.  Again, relaying is a different
matter entirely.

> In most cases, postfix is an intermediary MTA, handing the e-mail off
> to an LDA like a POP or IMAP server, (or Exchange, etc.) ...

  Technically speaking, an LDA (Local Delivery Agent, a subcase of MDA
(Mail Delivery Agent)) would be something like procmail or maildrop.
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.  Or maybe they've defined another term for
those that I'm not aware of yet.

  Exchange itself will never be an MDA for a Sendmail or Postfix
system, since you're going to have to do an SMTP relay to get the mail
into the Exchange system.  So the MDA would be the SMTP relay function
(the "smtp" mailer for Sendmail).

> It sounds like you're used to an Exchange environment where one
> "product" (Exchange) actually consists of several different
> components; the MTA, the LDA, the DNS server, the addressbook (which
> is called Active Directory, but is really "just an LDAP server"), the
> calendar manager, and the coffee machine all rolled into one.

  That's not really accurate or fair.  Indeed, for most people, the
distribution ("Red Hat Linux", "Debian GNU/Linux", etc.) is the
"product", and provides far more functionality than Exchange ever
will.  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.

  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.
There is something called the "MTA", but it doesn't do what an SMTP
MTA does.  Basically, once the SMTP service receives the mail into
Exchange, it gets converted into something that smells a lot like
X.400, and all the SMTP concepts go right out the window.

-- Ben