PMTU Discovery???

Tanya N kessler audiocollage at
Sun Mar 6 13:20:51 EST 2005

Alright, looks like I found the problem.  Seems SBC Yahoo is now blocking port 25 when sending mail to mail servers outside the domain.  I didn't have this problem a week ago, threw me for a loop.  I was able to sendmail to my SBC Yahoo email account from my email server, but no where else.  Looks like SBC Yahoo DSL users can request to open port 25 on their individual SBC accounts.  Thanks for all the help...

Cristian Mitrana <cristian.mitrana at> wrote:
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=, 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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