On 2007-12-13 at 07:31 +0100, zbigniew szalbot wrote:
> zbigniew szalbot pisze:
> > Thank you Peter - thinking about it, I must admit that at that time
> > the line must have been pretty choked (time to send some 2K emails
> > each about 70KB in size). This could have made it difficult to
> > properly connect and send data to o2.pl. I know exim behaved as
> > expected under given circumstances. To my knowledge o2.pl does not use
> > any greylisting (at least none that I am aware of). Could the reason
> > be bandwidth problems and would/could limits in bandwidth use help me
> > avoid such issues in future? Or is it the fault of the o2.pl server?
> I now have more information from the o2.pl server admin. They say they
> give 500 error code "when a line in the SMTP protocol extends to more
> than 1024 characters which we treat as not respecting the SMTP protocol
> standards."
>
> I have always thought that exim was very standard-compliant. Could you
> share your thoughts on this? Thank you!
Zbigniew, you haven't provided your Exim configuration, but I suspect
that what is happening is that these 70KB files are binaries being sent
as raw binaries, so there are no newlines. This is only a suspicion and
might easily be wrong.
The SMTP server acting as MX for o2.pl advertises 8BITMIME, so they will
accept binary attachments, but the sending MTA (yours) needs to pass
BODY=8BITMIME on the MAIL FROM line.
Exim does not support 8BITMIME; Exim is 8-bit clean and if given 8-bit
raw data will pass it on, unmolested, but supporting 8BITMIME requires
advertising 8BITMIME yourself and either accepting-then-bouncing when
sending an 8BITMIME message on to a site which does *not* advertise
8BITMIME (which has a startup problem for migrating) or having the MTA
perform MIME conversion automatically (which is not believed by Exim's
creator to be something that an MTA should do and also breaks
cryptographic signatures).
So why would Exim be trying to send on such a binary message? There are
two possibilities:
(1) You have "accept_8bitmime" turned on; this is not a good idea. It
should only be enabled on Exim boxes which receive mail but don't
send it out except to other boxes which are 8bitclean. Exim only
supports the SIZE and AUTH modifiers on outbound email.
(2) Some mail client is badly broken and sending 8bit data even when
the server doesn't support it, instead of using base64 encoding.
I've even seen mail-clients where the authors decided that they
didn't need to worry about standards and had deliberately decided
that they wouldn't use base64 for sending. :^(
So, check to see if these rejected mails are binary attachments not
encoded with base64. If they are, either fix your Exim config or fix
the mail-client config.
It might be that you have non-binaries with very very long lines; that
too is against the mail specifications, but Exim just passes along what
it's given, unmolested.
If this isn't the problem, then I'm sorry for wasting your time.
-Phil
