dotConnect for Salesforce Marketing Cloud (former ExactTarget) allows adding custom fields to the Subscriber object. dotConnect for Salesforce Marketing Cloud allows working with these fields in the same way as with predefined subscriber fields.

Additionally ExactTarget allows creating custom objects called data extensions. dotConnect for Salesforce Marketing Cloud determines whether to enable access to these objects depending on the SupportExtensionObjects connection string parameter (enabled by default). You can set it either directly via the ConnectionString property of ExactTargetConnection or via the SupportExtensionObjects property of ExactTargetConnectionStringBuilder. If this parameter is set to true, dotConnect for Salesforce Marketing Cloud will read data extension information and process data extensions in the same way as predefined ExactTarget objects. Note that custom Subscriber fields are not affected by this connection string parameter, they are always available in the same way as predefined Subscriber fields.

Note that reading data extension information can take additional time. If you don't need to work with data extensions, it's better to disable their reading by setting the SupportExtensionObjects connection string parameter to false.

For more information about ExactTarget data extensions see the ExactTarget documentation.