ITEM: BQ1579L
sendmail trouble connecting to AOL (America OnLine)
Problem:
sendmail trouble connecting to AOL (America On-Line)
When you try to send mail to aol.com
mail gets backed-up ..sendmail is returning messages to sender
claiming that the host "aol.com" does not exist
Problem lies with the prolific number of AOL.COM's MX records..
NSLOOKUP output (1st query):
> aol.com
Server: ausname1.austin.ibm.com
Address: 129.35.17.2
Non-authoritative answer:
aol.com preference = 25, mail exchanger = a.mr.aol.com
aol.com preference = 25, mail exchanger = b.mr.aol.com
aol.com preference = 25, mail exchanger = c.mr.aol.com
aol.com preference = 25, mail exchanger = d.mr.aol.com
aol.com preference = 25, mail exchanger = e.mr.aol.com
aol.com preference = 15, mail exchanger = a.mx.aol.com
aol.com preference = 15, mail exchanger = b.mx.aol.com
aol.com preference = 15, mail exchanger = c.mx.aol.com
aol.com preference = 15, mail exchanger = d.mx.aol.com
aol.com preference = 15, mail exchanger = e.mx.aol.com
aol.com preference = 15, mail exchanger = f.mx.aol.com
Authoritative answers can be found from:
aol.com nameserver = HP81.PROD.AOL.NET
aol.com nameserver = OPS01.OPS.aol.com
aol.com nameserver = DNS-AOL.ANS.NET
a.mr.aol.com internet address = 198.81.11.72
a.mr.aol.com internet address = 198.81.11.35
b.mr.aol.com internet address = 198.81.11.73
b.mr.aol.com internet address = 198.81.11.36
c.mr.aol.com internet address = 198.81.11.37
c.mr.aol.com internet address = 198.81.11.74
d.mr.aol.com internet address = 198.81.11.47
d.mr.aol.com internet address = 198.81.11.75
e.mr.aol.com internet address = 198.81.11.76
e.mr.aol.com internet address = 198.81.11.63
HP81.PROD.AOL.NET internet address = 192.203.190.18
OPS01.OPS.aol.com internet address = 152.163.80.11
>
NOTICE: several rotations are necessarry to the above response
(iterative calls to MX records for "aol.com" )
when the above combination returns...notice the "preference" then notice
the addresses..(no match)
Customer believes that it is during these episodes that the mail
notices come back about "aol.com does not exist"
Research located PMR \# 1412X,49R where similar problem with
aol.com and MX records resolved for AIX 3.2.5 by PTF's...
PTF's will be: U442576 U442608 U443467 U444240 U416967
(see PMR \# 1412X,49R)
Customer called in to say that the PTF's apparently fixed this
problem with AOL's MX records.
It's a pervasive problem with the way that AOL.COM has
setup the MX records for the AOL.com domain. Short recap of the
problem:
AOL.com has so many MX gateways listed, and each of these has
so many IP addresses associated with them, that the room in a single
UDP packet (limited to 512 bytes) used by DNS - will leave some of the
addresses out of the packet (too many to fit). When sendmail does a
lookup of type "MX"..(to find the domain's mail exchange) the DNS
packet reply from the nameserver will contain valid IP's for the MX's
shown about 90% of the time, -however 10% of the time the rotation of
addresses that DNS uses, will leave the packet devoid of some of the
addresses, and after so many iterations, you will get a packet back
that is missing the addresses for the first listing of the preferred
(lowest cost) mail gateway(s). Sendmail will queue the mail for the
next attempt. HOWEVER: when mail volumes are high enough to keep
sendmail constantly trying to send more and more messages to this same
(AOL.com) domain, then many sendmail forks are produced (the 10% that
fail), depleting resources on the machine..the customer will notice
all of these forked sendmail's in memory (trying to connect to
AOL.com) -and this becomes the issue.
Support Line: sendmail trouble connecting to AOL (America OnLine) ITEM: BQ1579L
Dated: January 1997 Category: N/A
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