So this is something that comes up every so often and I’m no sure where I learned it from many moons ago, but it has help me track down some SMTP addresses I can’t find searching AD or Exchange sometimes. It seems it’s not in use, but then I will try and create a new account with it or add an additional SMTP address to an existing account and I get the dreaded:
Microsoft Exchange Error
The following error(s) occurred while saving changes:
The proxy address “smtp:firstname.lastname@example.org” is already being used by “mycompany.local\users\user.name”. Please choose another proxy address.
In order to track this down, I use ADUC. First I create a new Query in “Saved Queries.” I then name is something like “Hidden SMTP” with a short description. I use the highest level root (since I don’t have a clue where it is) and include sub-containers.
I then click “Define Query…” and in the “Find” field (dropdown), I select “Custom Search.” Select “Advanced” and enter the following in the blank field:
Hit “Ok” and “Ok” again to bring you back to the ADUC MMC.
Under “Saved Queries,” you should see “Hidden SMTP” (or whatever you named the search).
Click on “Hidden SMTP,” then right click on the object and select “Refresh.” on the right pane, you should see the display name of where the object exists, the “name” of the object, the “Type” of object the email address is associated with, the “Exchange Alias,” and the “E-mail Address” to verify it is the right one you are looking for.
I have found this most useful when it pertains to email addresses assigned to a mail-enabled public folder. These can be the hardest to track down at times.
Good luck hunting…