Bug#567876: DKIM-related failures should not end up in the panic log

[Florian Weimer]

* Andreas Metzler:

> This was also discussed upstream, ending with:
> ----------------------------------------------------------
> On 2009-12-18 Kerstin Espey wrote
>> Am Donnerstag, 17. Dezember 2009 schrieb Tom Kistner:
> [...]
>>> Looking through the code, these are the most likely causes for the
>>>  failures:
>  
>>> 1) The message has more than 512 headers.
>>> 2) The message contains a single line longer than 16k bytes.

> ----------------------------------------------------------
>
> Looks like restricting the error to main_log is the right thing to do.

Thanks for tracking this down.

Can this be used to bypass DKIM-based filters?  This would be a bit
problematic.