Tag Archives: Exchange

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.