Have you reached your international Cap
If looks like you can't even ping smtp.isdsl.net (either one) very well from some IS accounts. Some accounts work, some dont. I think it depends whether you have reached your international cap. Response times just to ping it seem to range betwen 600 and 5000ms on the slow accounts, and 50ms on the quick ones.
I am curious to know whether all the people who are having this problem have reached their international cap?