[Exim] FYI Setting the ECN flag in TCP headers can prevent c…

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Szerző: Steve Bates
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Címzett: 'exim-users@exim.org'
Tárgy: [Exim] FYI Setting the ECN flag in TCP headers can prevent connection to some mail hosts.
I've just fixed a long running problem I've had running exim on RH7.2
It seems that the 2.4.18 kernel that was running on this box was setting the
TCP flag ECN on.
This prevented it from connecting to the following hosts:
mobile.att.net
easycare.com
cox.com
tdsecurities.com
airgatepcsa.com
BCBST.com
cmocanada.com
lewcosec.com
davidsbridal.net

99% of other hosts worked fine.

I had worked around the problem by routing the mail to another mail server
which could reach these hosts.

The problem can be solved by adding
net.ipv4.tcp_ecn = 0
To sysctl.conf

This turns off the ECN flags and everything started working again.

Steve Bates



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