- Open Microsoft Office 365 admin Centre
- Open Exchange Admin Centre from the left
- Click mailboxes on the left
- Find the users in the list (do not use search) and tick them on the left of their name
- On the top click Mailbox Policies
- Under Retention Policy select the policy you want to apply
- Click Save
- Once Saved Press the X (Close)
- The Retention Policy has now been applied.