One of my Exchange 2007 user encountered this error “The proxy address..is already being used by…. ” while trying to add a new SMTP email address to an existing mailbox account and it failed. He mentioned that the new SMTP address has never been assigned to any other mailbox in the organization.
Full Error:- The proxy address “smtp:email@example.com” is already being used by “contoso.com/Microsoft Exchange System Objects/my-Folder”. Please choose another proxy address.
The user mailbox is hosted on an Exchange 2007 mailbox database.
I suspect one of the public folder child item could be using this SMTP address, either it’s still in use or it’s orphaned.
To troubleshoot, I used ADSIEdit.msc tool to find the Exchange object causing the error, and under the attribute “class” it is marked “Public Folder”, on the properties dialog, I could see under “proxyAddresses” , the email address in the error was listed there.
Next is to use the tool PFDAVAdmin for exchange 2007,
Using PFDAVAdmin I was able to connect to the public folders in the organization and find one of the subfolders that was using the SMTP address shown in the error.
I requested user to choose another SMTP address, just as the error prompt suggested, and that solved it.
If the Exchange object is already orphaned and no longer in use in your organization you can delete it or rename the proxy-addresses attribute.
NOTE:- You can specify SMTP address spaces or non-SMTP address spaces on Send connectors that are configured on Hub Transport servers. You can only specify SMTP address spaces on Send connectors that are configured on Edge Transport servers.
<smarthosts> parameter This parameter takes one or more FQDNs, such as server.contoso.com, or one or more IP addresses, separated by commas. If you enter an IP address, you must enter the IP address as a literal as follows, for example: 10.10.1.1. The smart host identity can be the FQDN of a smart host server, a mail exchange (MX) record, or an address (A) record. If you configure an FQDN as the smart host identity, the source server for the Send connector must be able to use DNS name resolution to locate the smart host server. (https://msdn.microsoft.com/en-us/subscriptions/aa998294(v=exchg.80).aspx)
To do this via Exchange Management Console in Exchange 2010:- Click on Hub Transport -> Send Connectors -> double click on your send connector -> Network -> under route mail through the following send connector, edit to add the new IP and remove the old one if needed. Ok to accept changes, check that the new IP is added. Test and do a telnet to your new smarthost IP.