show us a screenshot of where its greyed out,
What should happen is this
1. You add your domain and exchange servers in the VAC
2. You add your provisioning and archiving tasks
3. You set up a provisioning group for the users you want to enable for archiving
4. You hit the enable mailbox button and you will choose your exchange server to enable from
5. You will then have a choice to enable new mailboxes or disabled mailboxes.
At this point if you don't see any mailboxes either new or disabled, you've either not provisioned correctly, or you've chosen an exchange server with no users
so either choose a different exchange server OR run the provisioning task and review the report to see who got provisioned and who didn't OR set a new exchange server up as a target in the VAC then run the provisioning task and then try to re-enable the mailbox
its also quite likely you might not even have a provisioning task set up due to the fact that in a journaling only scenario you don't have one
https://www.linkedin.com/in/alex-allen-turl-07370146