PMTU Discovery???

Cristian Mitrana cristian.mitrana at
Sun Mar 6 02:25:58 EST 2005

Tanya N kessler wrote:

>Hello All,
>I know this isn't directly related to Cyrus IMAP, but
>I thought maybe you could help.  I recently setup
>Cyrus IMAP with Sendmail using sieve on an FC3 box.  I
>can successfully send mail to certain domains while at
>the same time fail to send mail to other domains. 
>I've been digging through the web and found something
>about PMTU problems with ADSL.  I am using ADSL.  It
>seems that my connection just times out.  Here is my
>Mar  5 11:21:47 server sendmail[7070]: j23H8TtI004864:
>to=<fooman at>, delay=1+23:13:14,
>xdelay=00:00:00, mailer=esmtp, pri=4351863,
>, dsn=4.0.0, stat=Deferred:
>Connection timed out with

 Hotmail is very slow to respond on smtp, you might
try to increase the connect timeout. I had to to that
but I'm using postfix so the setup is different.

 For PMTU problems I use on the linux router an iptables rule like this:
iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -o $INETIF --match 
tcpmss --mss 1400:1536 -j TCPMSS --clamp-mss-to-pmtu
In my case some web sites were timing out when connecting with the browser
( for instance).

>I get this message for a couple of domains.  The whole
>thing is kind of funny, because not even a week ago I
>could send out mail to any domain with no problems. 
>Can anyone shed some light on this problem???

 If you had  the same ADSL connection back then I would
guess that you want to change the smtp timeout for sendmail
since it is not PMTU related.

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