contact ID

In the documentation it says, that the syntax of the contact ID should be like this: CID:ID02 but i have inserted only this: ID02 and it worked fine. is it important to include "CID:" ? This email and its attachments may be confidential and are intended solely for the use of the individual to whom it is addressed. If you are not the intended recipient or authorized to receive information for the intended recipient you are notified that disclosing, copying, distributing or taking any action in reliance on the contents of this information is strictly prohibited. If the email contains proposals, they are valid for 30 days following the date of email transmission. Finally, the recipient should check this email and any attachment for the presence of viruses. The company accepts no liability for any damage caused by any virus transmitted by email.