On Fri, 2022-04-29 at 10:56 +0100, Graeme Coates via Exim-users wrote: > Hi all, > > > > I've seen this issue raised in: > > > > https://lists.exim.org/lurker/message/20220216.071725.892984cd.en.html > > and > > https://lists.exim.org/lurker/message/20220313.200645.624cc373.en.html > > > > but haven't seen a definite resolution as yet. > > > > As per other reports, I have a Debian Bullseye (11.3) system running >
This is likely to be the result of a known issue with Google's TCP Fast Open setup - see e.g. https://blog.apnic.net/2021/07/05/tcp-fast-open-not-so-fast/ Exim 4.93 changed the default for the "hosts_try_fastopen" transport option to be "*", and the default for the net.ipv4.tcp_fastopen_blackhole_timeout_sec sysctl changed from 3600 (i.e. an hour) to 0 at some point between the kernel versions in Debian buster (10) and bullseye (11). A workaround is to add something similar to "hosts_try_fastopen = ! *.l.google.com" to your SMTP transports. Regards, Adam -- ## List details at https://lists.exim.org/mailman/listinfo/exim-users ## Exim details at http://www.exim.org/ ## Please use the Wiki with this list - http://wiki.exim.org/
