We had with our PC, where one Cllr refused to use our .gov email address, and demanded everything be sent to his personal email. He even signed a disclaimer to that effect, including a warning that should a FOI request come in, he may have to hand over all his emails, including personal ones. We sought advice from the ICO over the wording to make sure that we were correct on that one.
Winding on about 18 months, and we were subject to a rather nasty FOI. We tried to resist, but the ICO strongly implied that we had to comply, and if we didn't, they would rule against use. We were also informed in no uncertain terms that would and did include all his personal emails, in case he was trying to hide something: the fact that he was using his personal email address the complainant informed the ICO of!
Wind on about 18 months and a couple of hours.....and he resigned to stop this.
As a result any and all new councillors have to use the .gov.uk one, either via outlook or webmail, or receive all material via snail mail (or may collect in person from the Clerk).