Exim times out when trying to connect to some hosts, though those hosts are known to be up and running. Whats the problem?
A0068: There could be a number of reasons for this (see also Q0017). The obvious one is that there is a networking problem between the hosts. If you can ping between the hosts or connect in other ways, the problem might be caused by ECN (Explicit Congestion Notification) being enabled in your kernel. ECN uses TCP flags originally assigned to TOS – it’s a “new” invention, and some hosts and routers are known to be confused if a client uses it.
