postfix + dsl problem sending to hotmail and yahoo

I am having problems sending mail from postfix on a dsl connection, to
hotmail and yahoo

My configuration has not changed for at least two months, my IP is not
blacklisted anywhere, but hotmail's problems started about month ago and
yahoo was still working two weeks ago.

I get the following error message:

(host mx1.mail.yahoo.com[64.156.215.8] said: 501 Syntax error in
parameters or arguments (in reply to MAIL FROM command))

(host mx1.hotmail.com[65.54.166.99] said: 501 Invalid Address (in reply to
MAIL FROM command))

I can think of two posible problems:
1) I do not have the reverse DNS set up (and was not planning on doing so,
just to try to reduce the spam) 2) yahoo and hotmail are blocking mail
from dsl and dial up connections.

Can anyone shed some light onto this?

TIA

On Fri, 11 Jun 2004 13:07:36 -0400, verzonnen wrote:

>(...)
> I get the following error message:
>
> (host mx1.mail.yahoo.com[64.156.215.8] said: 501 Syntax error in
> parameters or arguments (in reply to MAIL FROM command))
>
> (host mx1.hotmail.com[65.54.166.99] said: 501 Invalid Address (in reply to
> MAIL FROM command))
>
> I can think of two posible problems:
> 1) I do not have the reverse DNS set up (and was not planning on doing so,
> just to try to reduce the spam) 2) yahoo and hotmail are blocking mail
> from dsl and dial up connections.
>
> Can anyone shed some light onto this?

One thing that can cause this problem: if the server name used in your
Postfix's HELO doesn't have a match in the DNS lookup. This can occur
if your Postfix installation uses the default (machine name) instead
of the domain name or server name in the HELO. Most mail servers
don't insist that reverse DNS works (IP address lookup is exactly the
same as the HELO name), because so many non-spam mail servers (like
netflix.com) are incorrectly configured and don't pass this test.
But many (most?) of them require that the reverse lookup returns
*something*. My system has worked just fine to hotmail & aol for
several years, from a business IDSL line... without the reverse-DNS
returning anything but the XO default name.

However, a subtle change in their config can cause their server
to stop accepting "mail.acme.com" if mail.acme.com isn't listed
in the DNS as the mail server for acme.com. Sometimes it works
better if the HELO is just the domain name, rather than the
actual server name. This probably contradicts some RFC or something,
but it usually works.

Also: the "501 Syntax error in parameters or arguments" error is
an error message that we started receiving one day from AOL, when
one of our clients changed a Perl library used by a mail-responder
Perl script. The new library left out some trivial thing in the
SMTP handshaking, and AOL rejected the mail with that USELESS error
message which doesn't give a clue WHAT the syntax error is, or
WHERE it occurs. We never found the exact problem, but it was
connected to Postfix's imitation of Sendmail.