Exim works fine on one host, but when I copied the binary to another identical host, it stopped working (it could not resolve DNS names).

Is the new host running exactly the same operating system? Most importantly, are the versions of the dynamically loaded libraries (files with names like libsocket.so.1) the same on both systems? If not, that is probably the cause of the problem. Either arrange for the libraries to be the same, or rebuild Exim from source on the new host.

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