From an Exim manual:
The so-called `percent hack' is the feature of mailers whereby a local part containing a percent sign gets interpreted as an entire new address, with the percent replaced by @. This is used for explicit mail routing and sometimes for testing. In Exim, it is possible to configure which local domains, if any, allow the `percent hack', though this is not recommended. Such usage, if configured, is, however, subject to the relay controls.
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So I suppose that means that I can e-mail
bjorn@gmx.de via an Oxford mail server by posting to bjorn%gmx.de@noriel.ox.ac.uk, providing that oriel's servers are configured to do such redirecting and providing that gmx's don't dump such mail on arrival as suspected spam. Hmm, I'll have to play .. with my own machines of course!
Regards,
Knöchlein Grete.
