It is usually a pain in the butt to figure out how to find the DN of a user and I can never remember how I did it; Fortunately I stumbled across this link which gives the following advice:

 

You may be asked to define a DN so that a service can bind to it to authenticate a query. Each user in Active Directory has a distinguished name. However, you cannot find it through the ADUC tool.

From a command prompt on your domain controller type: ldifde -f c:\export.txt

View the export.txt file in Notepad and do a find on the username. For example, you do a find on username zimbrauser. You will see something like this:
CN=zimbrauser,OU=External,DC=exonline,DC=intranet

 

This means that zimbrauser is in the OU called External in your AD forest exonline.intranet.

 

This worked beautifully for me. I’ll admit that it is a bit of a kludge, but damn… it’s so simple.

 

As usual, if this was helpful, leave a comment telling me so.