PMTU Discovery???

Craig White craigwhite at
Sat Mar 5 15:15:38 EST 2005

On Sat, 2005-03-05 at 08:56 -0800, 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
> maillog:
> 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
> 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???
lots of systems don't accept mail from smtp hosts that don't resolve via
dns - I have no idea if this is your problem or not. You might want to
see if your server/ip_address is listed in some RBL db - try searching
it in the database at

you can always try to telnet directly to a mail exchanger and conducting
a session interactively to see what it is saying and of course, you can
increase your logging level on sendmail (I believe you can manually edit
to loglevel 15 - by editing the directly)


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