[CentOS] Re: Sendmail and pmtu discovery

Sean Carolan scarolan at gmail.com
Tue Oct 28 16:20:42 UTC 2008

> Yes, I've dealt with these people.  If they turn off all ICMP, they often
> drop fragments as well, making the problem even worse. You can sometimes get
> them to listen by asking them if their Internet access seems a little
> "weird" in that some sites work sometimes or downloads are slow or they
> can't get some email :-)

What do you do when the receiving server is at Microsoft?  (mx4.hotmail.com)

Oct 28 11:18:25 exmx2 sendmail[19190]: m9SGHXL4019186:
to=<some.user at hotmail.com>, delay=00:00:52, xdelay=00:00:52,
mailer=esmtp, pri=43523, relay=mx4.hotmail.com. [],
dsn=4.0.0, stat=Deferred: Connection reset by mx4.hotmail.com.

I'm not surprised that Microsoft would make such a boneheaded decision
as to block all ICMP traffic to their hotmail servers, however would
this not cause a ton of customer email to simply be lost?  Do they
just not care?  I guess at this point my only choice may be to lower
my MTU size.

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