Closing CERN computer accounts
The CERN email account will be closed at the same time as your computer account. Therefore you should be able to have access to your emails through http://mmmservices.web.cern.ch/mmmservices/ up to two weeks after your contract end.
The standard procedure is to close your summer student account 2 weeks after the end date of your contract with CERN.
If you require files related to your work at CERN, then you should discuss this with your supervisor and arrange that the files are copied elsewhere (e.g. to a Internet Service Provider or to a CD or other media).