Todd Lyons wrote: > On Mon, Aug 9, 2010 at 11:21 PM, r00f <[email protected]> wrote: >> Well, thank you for tip but looks like ECN wasn't enabled on that host >> >> #sysctl -A | grep ecn >> net.ipv4.tcp_ecn = 0 > > I'm having an issue with a particular site being unable to send emails > that are larger than about 40K. And same configuration here, ECN not > enabled on either the load balancers nor the mail servers. > >> Servers negotiate TCP session with MSS 1360. Then they start SMTP session, >> which goes normal during HELO. But when the sending server sends me >> message >> headers, I receive: > > I'm having trouble with one site sending to my exim servers. They use > a Barracuda firewall. We have lots of people who send to us, and they > send out to lots of people. We just experience problems when he's > sending email to me. On my side, I see large gaps inbetween packets > that are sent. On their side, they see lots of TCP retransmissions. > It appears that, for those retransmitted packets, my side never gets > that first packet. > > The MTU is 1390 bytes for this particular host (seems to be 1420 for > most everybody else). I can find nothing that is causing this.
Grep the list archives. ISTR an issue two or more years ago wherein some (many?) broadband providers were - in essence - 'stealing' bytes for one overhead reason or another, AND ICMP was now-and-then firewalled (or ignored?), so the hosts could not negotiate a mutually useful MTU size - at least for anything that needed a full MTU (HELO and other basic 'handshakes' would not, but headers probably would, 'DATA' almost always would do...). Not (exclusively) an Exim issue - it's 'sub-optimal' configuration of the underlying TCP/IP... ... but it sounds familiar. HTH Bill Hacker > If > you find anything in your case, please do detail it as it could be > related to my case. > -- ## List details at http://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/
