Author: Evgeniy Berdnikov Date: To: exim-users Subject: Re: [exim] MS 365 "X-Matching-Connectors" header bounce error
Hello.
On Mon, Dec 13, 2021 at 04:49:01PM +0000, Graeme Fowler via Exim-users wrote: > On 13 Dec 2021, at 15:13, Evgeniy Berdnikov via Exim-users <exim-users@???> wrote:
> > Finally outlook.com reports 32799 bytes in a single header, while
> > the original mail has size 1216. So your Exim has modified message,
> > probably filling it with some garbage...
> >
> > As you run some customized configuration, your custom code should be
> > inspected for header/body manipulations.
>
> I’ve just done a very cursory Google search for that header
> name. There are a number of reports of the same error from different
> places, using different software (Postfix in one case), all of which
> tend toward this affecting a small and specific subset of message
> types (missing MIME headers, no content-type encoding for example)
> that are being handled by a smallish set of inbound Exchange Online
> servers, mostly in Europe.
Well, it could be easily checked disabling TLS for relevant transport
and recording a traffic dump for outgoing mail. If mail is not damaged
but outlook.com reports an error "ovesized header", then problem is
definitely on Microsoft's side.
However, problem could disappear in case of disabled TLS. :)
> You’ll have to get a recipient with a Microsoft contract to raise it for you.
It's better to do preliminary analysis on your own and get a proof that
your system behaves as expected. If you present a traffic dump, MS has
no way to blame client's side and reject the report.
--
Eugene Berdnikov
