Quoting Philip Hazel:
> As soon as a server starts processing a TCP/IP connection, this variable is
> Perhaps I should add the word "incoming", just in case it isn't obvious.
I'd say so. There were some people on the list stumbling over that, so
it seems to be not that obvious. Probably even in detail, like "It is
not set on outgoing connections, as Exim does not know the address the
OS will choose."