[linux-elitists] Postfix vs Exim

Marc MERLIN marc@merlins.org
Sat Sep 21 22:45:09 PDT 2002

On Sun, Sep 22, 2002 at 02:37:15PM +1000, Jeff Waugh wrote:
> <quote who="Marc MERLIN">
> > - I know  that because postfix isn't  monolithic like exim, and  that one of
> >   the prices to pay is that it doesn't do deduping (i.e. if a message is
> >   sent to you and an email alias, you get two copies). If postfix's secure
> >   module approach has other drawbacks, I'm interested to hear them
> I'd call this a very peripheral feature for an *MTA*. You can do it in
> procmail or some MUAs.
Right, but  it doesn't  work if you  feed the message  directly to  Cyrus or
similar, and not that many MUAs allow deduping by message ID
Unfortunately, that was almost the single reason why postfix didn't replace
sendmail at google for instance.
> > - I have been told that postfix can  do content filtering and bounce at SMTP
> >   time (like exim4's ACLs) and after data (like exim's system_filter).
> >   Confirmation would be appreciated
> It can do header and bodychecks with regexps or PCREs, as well as sending
> off to pipe transports for more advanced stuff.


> > - I don't know  if postfix can do  fined grained ACLs like exim4  and do RBL
> >   rejects but only if the from  domain matches a string, the connecting host
> >   is in a  certain IP range, and  none of the receipients  is postmaster for
> >   instance. Is postfix that configurable?
> To a point, yes. There's a couple of patches to do some crazier things such
> as per-client restriction rules, etc.


> > - I don't think postfix can do SMTP callbacks or callouts like exim.
> >   Confirmation appreciated.
> Non-exim-jargon feature description, please.

Sorry. Description here:

> > - I'm not sure that postfix can do the equivalent of exim's local scan or
> >   sendmail's milters. Confirmation appreciated
> Apart from the header/content checks, it supports external transports and
> transport tables. This is far, far more scalable than milters and such.
> Rather than launching extra processes, etc., you send the mail to another
> transport via pipe, lmtp, smtp, yada.

Well, exim does this too :-)  but the idea of a milter or exim's local scan
is that you do it at SMTP time.
What you describe is  done after the mail has been  accepted, which is often
too late to bounce it.

> > - postfix has an extensive lookup cache, which is a huge advantage over exim
> >   if you are doing  ldap lookups (ldap is slow, and exim  will not cache the
> >   lookup longer than the process runs)
> You might want to research that a bit more, it's a religious issue. :-)
What do  you mean? I  checked that  exim won't  cache beyond  the life  of a
subprocess and a friend  who knows postfix well told me  the caching he used
to do with LDAP on postfix.
Are you saying that the caching isn't very good or that caching is bad?
> > - Exim is the only MTA I know that can create virtual aliases on the fly
> >   (i.e. mailman aliases)
> Sounds like a non-MTA feature in an MTA again. ;-)
Yeah. Sue me :-)
> > - Does postfix  support complete header  rewriting (on all the  headers, per
> >   header and with regular expressions), like exim does?
> No. (Why would an MTA need to do this, if it couldn't replace the
> configurability with a sensible feature?)
So you're  saying that  you'd need to  tell postfix to  pipe the  program to
something else that does all the rewriting?
> > - What other cool things can postfix do that exim can't?
> Postfix is an MTA first and foremost, "cool features" need not apply (this,
> in itself, is one of my favourite features of Postfix... it's crack free).

Fair enough, I respect that (I think I've gotten a bit rotten with some of
the toys I have in exim :-)

Thanks for your answers
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems & security ....
                                      .... what McDonalds is to gourmet cooking 
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