Error c10312e7 – “This e-mail address already exists in this organization.”

I’ve been struggling with this error whilst trying to add an additional e-mail address to one of our groups in Active Directory:

Microsoft Active Directory – Exchange Extension
This e-mail address already exists in this organization.
ID no: c10312e7
Microsoft Active Directory – Exchange Extension
Being the good MCSE that I am I initially tried following MS KB280765, this didn’t yeald any results. On a side note “Method Two” which involves installing Network Monitor and sniffing the packet is a complete joke in my opinion.

I had much greater results following the details below which is from Jim McBee’s blog but originally from some pointers on a newsgroup by Rich Matheisen.

“Using the Windows 2003 Active Directory Users and Computers utility, right click on the domain, choose Find. In the Find: dropdown list, choose “Custom Search” and in the In: dropdown list, choose “Entire Directory”. Click the Advanced property page and enter the following LDAP query (in my example, at least):

Click Find and you should find the object that already has that SMTP address.”

However for me once I found the culprit I was surprised to see that the group which had the proxy address wasn’t current Exchange-enabled !!! i.e. Pull up the properties in Active Directory Users and Computers and note there are no Exchange tabs.
Thus I had to do the following:

Simple Solutions:

  1. In ADUC Right-click the offending object->Click Exchange Tasks
  2. Select “Remove Exchange Attributes”
  3. As long as successful all should be done, otherwise see below.

Complicated Solution:

  1. Install the Windows Server 2003 Support Tools from the Win2003 CD
  2. Start->Run->ADSIEDIT.MSC – (Big disclaimer here – you can really do damage with this, so you’re on your own, don’t blame me!)
  3. Navigate to the object returned in the steps above. Right-click->Properties
  4. Find the proxyAddresses attribute, Click Edit.
  5. Remove the offending SMTP e-mail address.

23 responses to “Error c10312e7 – “This e-mail address already exists in this organization.”

  1. If you can’t find the offending addresses using the normal MS LDAP query tool then you may need to use ADFind ( to extract the contents of the Global Catalog to a text file and then search through that. I had the problem where email addresses had been attached to the Public Store and these are not found by the MS Query tool. ADFind was the key to finding the entries. After finding the location ADSIEdit should be used to remove the entries from the Public Store (with due caution of course).

  2. Thanks! Worked great. Problem was that a Public folder had been created with the same name.

  3. This is great posting! Worked like a charm! Thannk you so much for making the time to post it

    Best Regards

  4. Thank you for this great post!
    It solved the problem in a few minutes, makes me wonder why MS doesn’t post this solution rather than KB280765.

    Best regards

  5. Thanks! Very helpful! Had an email address hidden in an obsure user – hijinks of the previous administrator – no doubt he had a plan at the time :)…

  6. I wish I had read this 2 years ago when you posted it…this is worth keeping around. Thanks!

  7. exactly what I needed! Thank you so much for posting!

  8. Same here! Your post helped me find that elusive address. Thanks for sharing!

  9. Just an FYI, this error also deals with making exchange changes locally from your XP machine via the users and computers with the ESM plugin installed.

    If you have the Adminpak installed on your pc and then the Exchange tools installed into the Adminpak then this is part of your issue.

    Go to the server and make the AD update to the account and you will not receive this error. Update all recipient services on the ESM as well to make sure the new address shows in the GAL.

  10. Thanks for the ldap query, worked great. can also @* if you have more then one domain

  11. Thanks, worked a treat and resolved as issue with minimal time because of your fantasic posting.

  12. Great Post!

    I also looked at Microsofts KB and it did nothing.

    Thanks for saving me a lot of explaining to the affected user!

  13. Thank you very much for your information.

    my problem solved now

    Warm Regards

  14. That’s very good solution
    my problem solved now

    thanks and regards

  15. You rock, my friend. This worked perfectly.

  16. Thank you! I tried following that lame KB article too and that yielded no results. But your method totally worked. We had the same issue as another poster – a public folder with the same name.

  17. After all the time since you wrote this, thanks ….


  18. many many thanks!
    with custom serach about
    my problem solved now

    Warm Regards

  19. Awesome, solved my issue – thanks!

  20. Thanks. This worked like a charm.

  21. Sweet! I followed that same KB article… like the rest, it was a complete waist of time. F-U Microsoft! Thanks Joel!

  22. Worked a treat cheers!

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