The AdWords API allows you to manage a large number of accounts using a single login credential set. In order to determine which account to run a query against, a customer identifier is required. Previously we allowed the use of either client email address or client customer ID as account identifier. Using email addresses does not handle a number of situations, though, such as address change, multiple accounts associated with one email and others. In addition, AdWords accounts created with no email address are just not accessible by this identifier. In order to unify account identification we decided to remove support for email addresses as account identifiers starting with v201109. From this version onward only client customer IDs are supported by the AdWords API. Migrating to client customer ID Most applications managing more than one AdWords account hold account identifiers in some form of a local storage. In case your application uses client email addresses as identifiers, you will need to convert those to client customer IDs, or add an extra field for the IDs. In order to make this migration smoother, we’ve provided an example that demonstrates how to obtain a client ID for a given email address. This example is included in every client library and also available online. It is easy to change how you identify a client account when making API requests if you use our client libraries. Depending on the language you use, you will need to update the configuration file or constructor parameter to include clientCustomerId instead of clientEmail. In case you construct your queries manually, please refer to the SOAP headers documentation page for more details. We would like to remind you that all existing versions that support identification by email addresses are scheduled for shutdown in Feb 2012.