This is tolerated under the CERN Computing Rules, as set out in Operational Circular No. 5, as long as it is occasional, does not encroach on work time and does not overburden the electronic network. You should bear in mind that even private email correspondence can reflect upon CERN if it sent from your CERN account. You are therefore encouraged to set up a private email address for personal correspondence.
(personal use of CERN e-mail address)