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Subject: Re: Sendmail --> PostFix conversion
From: Brad Knowles (blkskynet.be)
Date: Tue Sep 19 2000 - 12:18:46 CDT

At 9:38 AM -0700 2000/9/19, Harry wrote:

> So, the more I check this out, the more it appears that the term 'drop-in
> replacement' for PostFix seems to contain a lot of artistic license...
> Seriously, to me 'drop-in' always meant that it will readily use all
> existing configuration files, in all the same locations, and will work just
> as what it replaces.

        There is no such thing as "truly identical". Even identical
twins have some portion of their DNA that is not perfectly identical
to that of the other. Hell, pick any two cells from the same person,
and I'd be willing to bet that the DNS won't be a perfect match
between them.

        Take the same person and clone them, and they won't be identical
-- even if you clone them from the moment of conception (thus,
effectively creating artificial identical twins), they won't grow up
in exactly the same environment (one of them will always have been
born first, one of them will always be the "original", etc...), and
they won't turn out to be perfectly identical people.

        Take any two atoms, and I'm sure you can find tiny little
differences between them that keep them from being perfectly
identical.

        If that's the kind of perfection you're looking for, you won't
find it. Hell, you won't even find it with sendmail, because the
configuration file format is likely to change with version 9.0.

> It appears to be pretty spiffy for any new installations (as I have tried
> and discovered), but a rather tedius cross-grade when one comes from an
> existing Sendmail installation - this also explains my earlier wonderment
> why no larger migration to PostFix has taken place yet, from SendMail.

        There are some larger issues that postfix has yet to address
before it can be considered to be a fully functional equivalent of
sendmail.

        As just one example, it needs to have a concept of being able to
flush a queue for a particular site, and not just flush the entire
queue.

        For another, it needs some sort of a macro processing language,
to be able to handle the situations where people want/need it to do
something it was not designed to do, but where source level
modifications are not desirable.

        That said, postfix is a close enough match that it will work for
95-99% of the people, and that's the most important thing.

> Honestly, since Sendmail still is the standard, it appears to me that some
> from of automated conversion tool would contribute greatly to a larger
> adoption.

        I don't think it would be possible to create a program that could
fully and perfectly parse sendmail.cf files (even if the purpose was
to then convert that to a different sort of configuration file),
short of writing a program that basically *is* sendmail, and then
you're back where you started from.

        Simply put, what you're asking for is just plain impossible to
deliver. It might be possible to create a Perl program that could
interpret the contents of a sendmail.mc file and then convert most of
that to postfix.

        You might even be able to write a program that could understand
most of the typical definitions made at the top of a sendmail.cf
file, and comprehend sendmail.cf re-write rules that are generated by
certain versions of the m4 macros that come with certain versions of
the sendmail package, but they'd be guaranteed to choke on anything
remotely unusual.

        Even that would only be an 80% solution for most sites, and it
sounds to me like sites like this are waiting to be fed applesauce
with a silver spoon and from a bowl made out of gold, resting on a
platter made out of platinum.

        Anyone in that category is going to be very, very disappointed
with the real world in general, and I'd recommend that they go back
inside where they came from and curl up for a nice long sleep. 

--
   These are my opinions -- not to be taken as official Skynet policy
======================================================================
Brad Knowles, <blkskynet.be>                || Belgacom Skynet SA/NV
Systems Architect, Mail/News/FTP/Proxy Admin || Rue Colonel Bourg, 124
Phone/Fax: +32-2-706.13.11/12.49             || B-1140 Brussels
http://www.skynet.be                         || Belgium

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