Is it necessary to ask contacts to confirm their consent?

The GDPR clarifies that if your company or organization collects data from European Union residents, you must retain proof of their consent to the collection and use of this data. However, the regulation does not specify what information constitutes "proof" (e.g. IP address, log, time of registration, etc.). 

You do NOT need to ask your contacts to confirm their consent if your collection and use of their data: 

If your contacts' consent is required and you do not have proof of their consent, follow this guide to confirm your contacts' consent.