Exim and parsing "unusual" Envelope Froms

Hi,

A client runs a Netware MHS to SMTP gateway. In certain circumstances
this gateway generates rather "unusual" envelope froms.

For instance:

wpuser%mhshost{"gwisedom1.gwisedom2:user"}@mhs.client.co.za

(The original MHS address was "wpuser@mhshost{gwisedom1.gwisedom2:user}")

Exim complains about this address, saying "@ missing in route address".

Is the SMTP address the gateway generates valid? Opinions around here are
mixed.

Thanks,
Steve