There's been no official communication about the specifics of CDC because it doesn't exist yet. RM are waiting on the necessary legislation and regulation to set up what will be the first CDC pension in the UK.
Unless something changes, CDC will replace all existing RM pension schemes.
The last official statement on a possible start date said they were hoping for the second half of the current(21/22) financial year.
More info can be found here: https://www.myroyalmail.com/2018pensionreviewqanda
You'll currently be in the RMDCP scheme managed by Scottish Widows, which is basically just a savings account with which you have options. One of which is to buy an annuity which provides an income for the rest of your life.I know that my recent pension statement said I'd be looking at a pension worth £31 per week (I'm 43) :)
There are other options with a Defined Contribution(DC) scheme, as this link will tell you: https://www.moneyhelper.org.uk/en/pensi ... on-schemes