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On 08/28/13 11:02, Oliver Hitz wrote:
On 28 Aug 2013, Michael Richter wrote:
Trying 195.186.227.50... Connected to mxzhh.bluewin.ch. Escape character is '^]'. 421 4.4.5 Service unavailable, concurrency limit reached.
We see the mail queues growing with undeliverable mails for bluewin.ch.
The same also happened on monday before Swisscom was unreachable. This reminds me of 2011 when they were attacked.
There was an attack and maybe it has amplified this issue but so far the root cause of the problem was a strange behavior of the bluewin MX load balancer (LB).
For unknown reasons, LB probes for MX server have failed although each MX server was running fine.
The LB started removing "failed" MX server from MXIN pool for several minutes. The pool got smaller and smaller. The load on the remaining pool was increasing until the concurrency limit was reached.
This issue was resolved at moon (GMT+2). An investigation is underway to find out how this happened.
Regards, Tom