The Mailing Preference Service (MPS) web service allows you to check whether an individual is registered with the MPS.
The MPS service can be accessed at http://webservices.data-8.co.uk/MPS.asmx.
To find out more you can use the below links
View Integr8 Web Services Overview
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Currently matching against 388,137,693 records, last updated 22/05/2012.