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.
You’ll have to get a recipient with a Microsoft contract to raise it for you.
