One of the most common requests for Exchange administrators is to find out who owns such SMTP address or if an SMTP address ever exist on your SMTP Domain. Those of you, who is performing troubleshooting daily bases will understand this right a away. The Classic way of verifying if, such SMTP address is valid or no would be opening outlook and pasting the address into "TO" column. If outlook resolves the address, it means address is valid (owned by an object within your SMTP Domain). If outlook puts underline on to the SMTP address, it means this mail address is not present within your environment. The more advance way of doing this would be opening up ADUC and going to search option , pasting the mail address in it, firstname.lastname@example.org, than we would expect this would return an object.
The most advance way of accomplishing same result would be
Start, Run, Dsa.msc, Click Search button, Click Drop down menu, select Custom search, Click Advance
In the LDAP Query write down below (change my mail address to one you need to lookup)
Adfind -b dc=SMTP25, dc=org -f (proxyAddresses=SMTP: oz*) name proxyaddresses
This will find all the SMTP Proxy address contains OZ.
We can also find the object with below switch; don't forget the Change my name to whatever the name you are looking within your search
Adfind -b dc=SMTP25, dc=org -f (samaccountname=oozugurlu)
ADFInd is fast and incredibly efficient, it is a free utility and if you have not get your hands on it don't lose a time go get it and start using it.