intermittent failures with sendmail

[Alex Teslik]

I have sendmail 8.14.2 running on freebsd 7.0:

[gouda:root]/var/spool/mqueue# sendmail -d0 < /dev/null
Version 8.14.2
 Compiled with: DNSMAP LOG MAP_REGEX MATCHGECOS MILTER MIME7TO8 MIME8TO7
		NAMED_BIND NETINET NETINET6 NETUNIX NEWDB NIS PIPELINING SASLv2
		SCANF STARTTLS TCPWRAPPERS USERDB XDEBUG

============ SYSTEM IDENTITY (after readcf) ============
      (short domain name) $w = gouda
  (canonical domain name) $j = gouda.acatysmoof.com
         (subdomain name) $m = acatysmoof.com
              (node name) $k = gouda.acatysmoof.com
========================================================

[gouda:root]/var/spool/mqueue# uname -a
FreeBSD gouda.acatysmoof.com 7.0-STABLE-200806 FreeBSD 7.0-STABLE-200806 #0: Mon Jun 30 
03:43:40 PDT 2008     alex at XXXXXXX.com:/usr/obj/usr/src/sys/CORE2-STABLE-7  i386

mails sent out to the internet are intermittently causing these error reports in the daily run output:

n5UNkYTo069809    23878 Tue Jun 30 16:46 <alex at XXXXX.com> 
                (reply: read error from mail.OOOOOO.net.) 
                         <rad at OOOOOO.net> 
n5ULKB0i064252* 7028205 Tue Jun 30 14:20 <kitty at BBBBBBBB.com> 
     8BITMIME   (timeout writing message to c.mx.mail.yahoo.com.: Broken pipe) 
                         <XXXXXX at yahoo.com> 
n5TM36Jn012370      420 Mon Jun 29 15:03 <XXXXXXX at acat 
                (Deferred: Name server: YYYYYYY.com.: host name lookup failur) 
                         <avalderrama at YYYYYY.com>


The yahoo one is particularly puzzling. Most mails make it, but some fail. I can't figure out why. The 
recipient is valid and they have plenty of space in their account. Sometimes mail to them works with 
no problem.

I checked the sendmail logs and found:

Jul  2 03:35:16 gouda sm-mta[40342]: n5ULKB0i064252: SYSERR(root): timeout writing message to 
b.mx.mail.yahoo.com.: Broken pipe
Jul  2 04:23:01 gouda sm-mta[47860]: n5ULKB0i064252: SYSERR(root): timeout writing message to 
e.mx.mail.yahoo.com.: Broken pipe
Jul  2 07:03:05 gouda sm-mta[53788]: n5ULKB0i064252: SYSERR(root): timeout writing message to 
d.mx.mail.yahoo.com.: Broken pipe

I thought it might be an MTU problem:

http://anthony.zerosandones.co.uk/?q=node/451

I set my MTU to 1300, but that hasn't helped.

[gouda:root]/home/alex/acatysmoof.com/services# ifconfig -a
em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1300
	options=19b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,TSO4>
	ether 00:1c:c0:36:85:62
	inet 24.205.141.134 netmask 0xfffffffc broadcast 24.205.141.135
	media: Ethernet autoselect (100baseTX <full-duplex>)
	status: active

DNS is working fine everywhere, so I don't think thats it. PTR is fine, reverse lookups work fine.

I've googled my brains out. Does anyone have any ideas?

Thanks,
Alex