After a user's mailbox is re-enabled in an Exchange 2016 or Exchange 2013 environment, the user can't access their mailbox by using one or more client protocols.
When a user account has the Exchange mailbox disabled, the following Exchange attributes aren't removed from the user object:
Use the Set-CASMailbox
cmdlet to enable the client protocol that's required for the user to connect to their mailbox. For example, to enable Outlook Anywhere for the user, run the following cmdlet:
Set-CASMailbox Jim -MAPIBlockOutlookRpcHttp:$False