I need to replicate the behaviour of what appears to be a closed method in the SharePoint object model.

The method is "microsoft.sharepoint.administration.spemailmap.assignalias" - which is called when you enter an email address in the incoming email settings of a list. It will check to see if the email is already in use. 

I have a site provisioning tool which needs to carry out the this same check before a site is created. I have an input text box which takes in the user input - however this needs to be checked against all registered email addresses.

Does anyone have a coded solution or alternative workaround for the above problem?