Q182821: XFOR: Internet Mail Service Not Trying Next Exchange Record
Article: Q182821
Product(s): Microsoft Exchange
Version(s): 5.0 5.5
Operating System(s):
Keyword(s): kbusage
Last Modified: 05-APR-1999
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The information in this article applies to:
- Microsoft Exchange Server, versions 5.0, 5.5
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SYMPTOMS
========
The Microsoft Exchange Server Internet Mail Service does not fail over to the
next Exchange record for a given domain, and the message is eventually returned
to the sender with a non-delivery report (NDR).
CAUSE
=====
The Internet Mail Service failed to try the next Exchange record if the host for
the first Exchange record accepted the TCP three-way handshake (Syn-SynAck-Ack).
STATUS
======
Microsoft has confirmed this to be a problem in Exchange Server version 5.0.
A supported fix is now available, but has not been fully regression-tested and
should be applied only to systems experiencing this specific problem. Unless you
are severely impacted by this specific problem, Microsoft recommends that you
wait for the next Service Pack that contains this fix. Contact Microsoft
Technical Support for more information.
This fix has been posted to the following Internet location:
ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixes/Eng/Exchg5.0/Post-SP2-IMS/
Microsoft has confirmed this to be a problem in Microsoft Exchange Server version
5.5. This problem has been corrected in the latest U.S. Service Pack for
Microsoft Exchange Server version 5.5. For information about obtaining the
Service Pack, query on the following word in the Microsoft Knowledge Base
(without the spaces):
S E R V P A C K
MORE INFORMATION
================
By examining a network trace of a computer exhibiting this behavior, you will
see the following conversation occur:
1. The Internet Mail Service queries the Domain Name Service (DNS) server for
the domain in question.
For example, in the following packet, a query has been generated to find all
Exchange records for SampleOrg.com, as can be seen in the DNS: Question
Section below:
+ FRAME: Base frame properties
+ ETHERNET: ETYPE = 0x0800 : Protocol = IP: DOD Internet Protocol
+ IP: ID = 0x6F0A; Proto = UDP; Len: 57
+ UDP: Src Port: Unknown, (1146); Dst Port: DNS (53); Length = 37 (0x25)
DNS: 0x5:Std Qry for SampleOrg.com. of type Mail Xchg on class INET addr.
DNS: Query Identifier = 5 (0x5)
+ DNS: DNS Flags = Query, OpCode - Std Qry, RD Bits Set, RCode - No
error
DNS: Question Entry Count = 1 (0x1)
DNS: Answer Entry Count = 0 (0x0)
DNS: Name Server Count = 0 (0x0)
DNS: Additional Records Count = 0 (0x0)
DNS: Question Section: SampleOrg.com. of type Mail Xchg on class INET
addr.
DNS: Question Name: SampleOrg.com.
DNS: Question Type = Mail exchange
DNS: Question Class = Internet address class
2. The DNS server returns the list of Exchange records it has for the domain in
question.
For example, in the packet, the DNS server responds as can be seen in the DNS:
Answer Section below. From this section of the packet, we know that the DNS
server knows of two Exchange records for SampleOrg.com: Server1 with a
preference of 100 and Server2 with a preference of 300.
+ FRAME: Base frame properties
+ ETHERNET: ETYPE = 0x0800 : Protocol = IP: DOD Internet Protocol
+ IP: ID = 0xC482; Proto = UDP; Len: 527
+ UDP: Src Port: DNS, (53); Dst Port: Unknown (1146); Length = 507 (0x1FB)
DNS: 0x5:Std Qry Resp. for SampleOrg.com. of type Mail Xchg on class INET
addr.
DNS: Query Identifier = 5 (0x5)
+ DNS: DNS Flags = Response, OpCode - Std Qry, AA RD RA Bits Set, RCode
- No error
DNS: Question Entry Count = 1 (0x1)
DNS: Answer Entry Count = 2 (0x2)
DNS: Name Server Count = 5 (0x5)
DNS: Additional Records Count = 2 (0x2)
DNS: Question Section: SampleOrg.com. of type Mail Xchg on class INET
addr.
DNS: Question Name: SampleOrg.com.
DNS: Question Type = Mail exchange
DNS: Question Class = Internet address class
DNS: Answer section: SampleOrg.com. of type Mail Xchg on class INET
addr.(8 records present)
DNS: Resource Record: SampleOrg.com. of type Mail Xchg on class
INET addr.
DNS: Resource Name: SampleOrg.com.
DNS: Resource Type = Mail exchange
DNS: Resource Class = Internet address class
DNS: Time To Live = 7200 (0x1C20)
DNS: Resource Data Length = 10 (0xA)
DNS: Preference = 100 (0x64)
DNS: Exchange Mailbox: Server1.SampleOrg.com.
DNS: Resource Record: SampleOrg.com. of type Mail Xchg on class
INET addr.
DNS: Resource Name: SampleOrg.com.
DNS: Resource Type = Mail exchange
DNS: Resource Class = Internet address class
DNS: Time To Live = 7200 (0x1C20)
DNS: Resource Data Length = 11 (0xB)
DNS: Preference = 300 (0x12C)
DNS: Exchange Mailbox: Server2.SampleOrg.com.
+ DNS: Authority Section: SampleOrg.com. of type Auth. NS on class INET
addr.(5 records present)
+ DNS: Additional Records Section: Server1.SampleOrg.com. of type Host
Addr on class INET addr.(2 records present)
3. The Internet Mail Service queries the DNS server for the Host information of
the Exchange record with the lowest preference value.
For example, in the following packet, a query has been generated to find the
Host Address for Server1.SampleOrg.com, as can be seen in the DNS: Question
Section below.
+ FRAME: Base frame properties
+ ETHERNET: ETYPE = 0x0800 : Protocol = IP: DOD Internet Protocol
+ IP: ID = 0x700A; Proto = UDP; Len: 64
+ UDP: Src Port: Unknown, (1147); Dst Port: DNS (53); Length = 44 (0x2C)
DNS: 0x1:Std Qry for Server1.SampleOrg.com. of type Host Addr on class
INET addr.
DNS: Query Identifier = 1 (0x1)
+ DNS: DNS Flags = Query, OpCode - Std Qry, RD Bits Set, RCode - No
error
DNS: Question Entry Count = 1 (0x1)
DNS: Answer Entry Count = 0 (0x0)
DNS: Name Server Count = 0 (0x0)
DNS: Additional Records Count = 0 (0x0)
DNS: Question Section: Server1.SampleOrg.com. of type Host Addr on
class INET addr.
DNS: Question Name: Server1.SampleOrg.com.
DNS: Question Type = Host Address
DNS: Question Class = Internet address class
4. The DNS returns the IP address of the server in question.
For example, in the following packet, the DNS server responds as can be seen
in the DNS: Answer Section below. From this section of the packet, you see
that the IP address of Server1 is 200.200.200.1.
+ FRAME: Base frame properties
+ ETHERNET: ETYPE = 0x0800 : Protocol = IP: DOD Internet Protocol
+ IP: ID = 0xC483; Proto = UDP; Len: 274
+ UDP: Src Port: DNS, (53); Dst Port: Unknown (1147); Length = 254 (0xFE)
DNS: 0x1:Std Qry Resp. for Server1.SampleOrg.com. of type Host Addr on
class INET addr.
DNS: Query Identifier = 1 (0x1)
+ DNS: DNS Flags = Response, OpCode - Std Qry, RD RA Bits Set, RCode -
No error
DNS: Question Entry Count = 1 (0x1)
DNS: Answer Entry Count = 1 (0x1)
DNS: Name Server Count = 5 (0x5)
DNS: Additional Records Count = 5 (0x5)
DNS: Question Section: Server1.SampleOrg.com. of type Host Addr on
class INET addr.
DNS: Question Name: Server1.SampleOrg.com.
DNS: Question Type = Host Address
DNS: Question Class = Internet address class
DNS: Answer section: Server1.SampleOrg.com. of type Host Addr on
class INET addr.
DNS: Resource Name: Server1.SampleOrg.com.
DNS: Resource Type = Host Address
DNS: Resource Class = Internet address class
DNS: Time To Live = 636 (0x27C)
DNS: Resource Data Length = 4 (0x4)
DNS: IP address = 200.200.200.1
+ DNS: Authority Section: SampleOrg.com. of type Auth. NS on class INET
addr.(5 records present)
+ DNS: Additional Records Section: ns.SampleOrg.com. of type Host Addr
on class INET addr.(5 records present)
5. The Internet Mail Service now initiates a TCP connection to Server1.
This is done with the following three packets, which is known as the TCP
three-way handshake (Syn-SynAck-Ack).
+ FRAME: Base frame properties
+ ETHERNET: ETYPE = 0x0800 : Protocol = IP: DOD Internet Protocol
+ IP: ID = 0x730A; Proto = TCP; Len: 44
+ TCP: ....S., len: 4, seq: 3447617-3447620, ack: 0, win:
8192, src: 1145 dst: 25 (SMTP)
+ FRAME: Base frame properties
+ ETHERNET: ETYPE = 0x0800 : Protocol = IP: DOD Internet Protocol
+ IP: ID = 0x292B; Proto = TCP; Len: 44
+ TCP: .A..S., len: 4, seq:2120192000-2120192003, ack: 3447618, win:
4096, src: 25 (SMTP) dst: 1145
+ FRAME: Base frame properties
+ ETHERNET: ETYPE = 0x0800 : Protocol = IP: DOD Internet Protocol
+ IP: ID = 0x740A; Proto = TCP; Len: 40
+ TCP: .A...., len: 0, seq: 3447618-3447618, ack:2120192001, win:
8760, src: 1145 dst: 25 (SMTP)
6. IMPORTANT NOTE: The following packet is never received in the failing case.
In a normal working situation (that is, there is an SMTP daemon listening on
Server1), the next packet contains the SMTP Service Ready banner. If Server1
does not send an SMTP Service Ready banner, the Internet Mail Service
continues to try this same Exchange record until the message times out and an
NDR is sent to the sender.
+ FRAME: Base frame properties
+ ETHERNET: ETYPE = 0x0800 : Protocol = IP: DOD Internet Protocol
+ IP: ID = 0x9485; Proto = TCP; Len: 118
+ TCP: .AP..., len: 78, seq:2034176001-2034176078, ack: 3332995, win:
4096, src: 25 (SMTP) dst: 1145
SMTP: Rsp: Service ready, 78 bytes
SMTP: Response = 220 Server1.SampleOrg.com Microsoft Exchange
Internet Mail Service 5.0.1458.49 ready
Additional query words: IMC
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Keywords : kbusage
Technology : kbExchangeSearch kbExchange500 kbExchange550 kbZNotKeyword2
Version : 5.0 5.5
Issue type : kbbug
Solution Type : kbfix
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