Well basically I was wondering how Death Eaters would send a message to a member of The Order?

I've racked my brians and I can't think of an instance, in any of the books, where Death Eaters have communicated with the Order (and vise versa) by owl or a message in the form of a patronus etc.

I'm assuming they avoid using owls to avoid revealing hiding places.

They couldn't send a person/messenger as they'd have to know the location of headquaters.

So what do you think could be used to get a message from one group to another?

Any help would be much appreciated