Integration with Professional Edition is supported when The Force.com SOAP API is enabled (https://help.salesforce.com/articleView?id=000005140&type=1) Essentials not supported. Professional is supported in Lightening mode, Enterprise is supported in Classic and Lightening mode, Unlimited is supported in Classic and Lightening mode.Salesforce 'Console' is not supported.Service Cloud - Integration is available with the tables i.e. contacts, accounts and leads only. Note, integration does not connect to the fields / tabs of ‘cases’ and ‘solutions’.
If the integration supports caching, please note that cached integrations support up to 30,000 contacts. The live mode method would need to be used for larger directories. Performance will then be determined by a number of additional factors including network speed and application API specification.