Duplicate SPN Issues with Exchange http/mail.domain.com issue

I have an issue with duplicate SPN's for http/mail.domain.com.  Here is the output of setspn -X:
http/mail.domain.com is registered on these accounts:
        CN=EXCHCAS2,OU=Production,OU=Servers,DC=domain,DC=com
        CN=EXCHCAS1,OU=Production,OU=Servers,DC=domain,DC=com

On the domain control I receive this error:
Log Name:      System
Source:        Microsoft-Windows-Kerberos-Key-Distribution-Center
Date:          5/20/2015 3:49:30 PM
Event ID:      11
Task Category: None
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      DS2.domain.com
Description:
The KDC encountered duplicate names while processing a Kerberos authentication request. The duplicate name is HTTP/mail.domain.com (of type DS_SERVICE_PRINCIPAL_NAME). This may result in authentication failures or downgrades to NTLM. In order to prevent this from occuring remove the duplicate entries for HTTP/mail.domain.com in Active Directory.
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Microsoft-Windows-Kerberos-Key-Distribution-Center" Guid="{3FD9DA1A-5A54-46C5-9A26-9BD7C0685056}" EventSourceName="KDC" />
    <EventID Qualifiers="49152">11</EventID>
    <Version>0</Version>
    <Level>2</Level>
    <Task>0</Task>
    <Opcode>0</Opcode>
    <Keywords>0x80000000000000</Keywords>
    <TimeCreated SystemTime="2015-05-20T22:49:30.000000000Z" />
    <EventRecordID>357842</EventRecordID>
    <Correlation />
    <Execution ProcessID="0" ThreadID="0" />
    <Channel>System</Channel>
    <Computer>DS2.domain.com</Computer>
    <Security />
  </System>
  <EventData>
    <Data Name="Name">HTTP/mail.domain.com</Data>
    <Data Name="Type">DS_SERVICE_PRINCIPAL_NAME</Data>
    <Binary>
    </Binary>
  </EventData>
</Event>

On all windows workstations with Outlook I receive this error:
Log Name:      System
Source:        Microsoft-Windows-Security-Kerberos
Date:          3/5/2015 5:35:17 PM
Event ID:      3
Task Category: None
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      computer.domain.com
Description:
A Kerberos error message was received:
 on logon session
 Client Time:
 Server Time: 1:35:17.0000 3/6/2015 Z
 Error Code: 0x7  KDC_ERR_S_PRINCIPAL_UNKNOWN
 Extended Error: 0xc0000035 KLIN(0)
 Client Realm:
 Client Name:
 Server Realm: DOMAIN.COM
 Server Name: HTTP/mail.domain.com
 Target Name: HTTP/mail.domain.com@DOMAIN.COM
 Error Text:
 File: 9
 Line: 12c4
 Error Data is in record data.
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Microsoft-Windows-Security-Kerberos" Guid="{98E6CFCB-EE0A-41E0-A57B-622D4E1B30B1}" EventSourceName="Kerberos" />
    <EventID Qualifiers="32768">3</EventID>
    <Version>0</Version>
    <Level>2</Level>
    <Task>0</Task>
    <Opcode>0</Opcode>
    <Keywords>0x80000000000000</Keywords>
    <TimeCreated SystemTime="2015-03-06T01:35:17.000000000Z" />
    <EventRecordID>129428</EventRecordID>
    <Correlation />
    <Execution ProcessID="0" ThreadID="0" />
    <Channel>System</Channel>
    <Computer>computer.domain.com</Computer>
    <Security />
  </System>
  <EventData>
    <Data Name="LogonSession">
    </Data>
    <Data Name="ClientTime">
    </Data>
    <Data Name="ServerTime">1:35:17.0000 3/6/2015 Z</Data>
    <Data Name="ErrorCode">0x7</Data>
    <Data Name="ErrorMessage"> KDC_ERR_S_PRINCIPAL_UNKNOWN</Data>
    <Data Name="ExtendedError">0xc0000035 KLIN(0)</Data>
    <Data Name="ClientRealm">
    </Data>
    <Data Name="ClientName">
    </Data>
    <Data Name="ServerRealm">DOMAIN.COM</Data>
    <Data Name="ServerName">HTTP/mail.domain.com</Data>
    <Data Name="TargetName">HTTP/mail.domain.com@DOMAIN.COM</Data>
    <Data Name="ErrorText">
    </Data>
    <Data Name="File">9</Data>
    <Data Name="Line">12c4</Data>
    <Binary>3015A103020103A20E040C350000C00000000001000000</Binary>
  </EventData>
</Event>

Exchange 2010 SP3 RU6 all servers are Server 2008 R2 Enterprise SP1

Any suggestions on how to resolve this? No one seems to notice that anything is going on other than error logs on the workstations and domain controllers.  I can trace it back to at least 6 months ago before the logs rollover.

Thank you.
LVL 1
bgib2610Asked:
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bvwbzbCommented:
I've had this a few years ago, geez, I cant remember exactly how, but I did delete it.. If I'm not mistaken, It could have been done via ADSIEDIT. perhaps go in there and browse to the location of this double reference and then delete one..
In ADSIEDIT you may find a larger structure than in AD, so just check, I cant recall from the top of my head, but you should be able to expand a few and then figure it out... either AD structure to the server's computer object, or within an exchange related location.. (leaning towards exchange location)

hope it helps,

regards
Bronwen

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bgib2610Author Commented:
I just delete it and started getting password prompts in Outlook.  I put it back in and the password prompts went away.
bgib2610Author Commented:
I deleted the other SPN and the issue went away.  I deleted the SPN on the wrong server the first time.
bvwbzbCommented:
cool, sorry, I missed your first one, but glad you got it resolved! :)
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