[linux-elitists] Postfix vs Exim
Sat Sep 21 22:57:28 PDT 2002
<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 just wouldn't be doing this in my MTA. I could let an MDA or another
transport do it, but it doesn't sound like a critical core feature.
> > > - I don't think postfix can do SMTP callbacks or callouts like exim.
> > > Confirmation appreciated.
> > Non-exim-jargon feature description, please.
> Sorry. Description here:
Hmm, it does every check up to this, not entirely sure if it will actually
attempt to connect and validate the email delivery though... Could be wrong.
> > > - 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.
I've been happy with the number of checks that postfix already offers
through the receive process. As well as the header/body checks, it now has a
data restrictions hook, but thus far I've only seen it used for rejecting
pipelining at that stage.
I'm sure Wietse has answered this a hundred times or more though, I'll peek
in the archives to see.
> > > - 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?
Caching can be bad, and there have been issues with client-side caching with
OpenLDAP, so there's a lot of FUD about it. There are definite plans to make
caching better with postfix though (sounded really cool last time I read
> > > - 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?
No, I'm wondering why you'd do header rewriting manually in the first place,
rather than adding a system to the MTA to handle common requirements for you
with sensible configuration options.
"She sped into the parking lot, the door flew open and there she was,
dressed only in a black bathing suit and sunglasses. I got in and she
reversed straight into another car. Classic Carine." - Stephen Gan
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