If you are an administrator of a Salesforce org, you might have received the reminder email about the EU4 site switch. The email states that your org might need to renew the DNS cache memory after the site switch has been completed. This reminder is not applicable for Connexys orgs. You and/or your organisation will not have to take action regarding the reminder email.
Be aware that the site switch will cause the orgs on the EU4 instance to have read only access during the switch. The switch will be done on Saturday December 5, 2015, between the hours of 07:00 and 19:30 (US pacific time).
To check on which instance your organisation operates, please visit this page, click on the question mark and enter the name of your domain.