Many thanks to Tony, Liam, Wayne and everyone else who helped get me going along my various stages of being stuck.

Basically, to achieve this domain / exchange migration it was pretty easy once I knew what I was doing.
The first and most important thing to use is the “Installing and Configuring” help file. (and maybe the Administrators Guide a bit).

Your first basic steps are just like setting up a new vanilla Vault site. Do all the things you would do for a brand new install only add your stuff for your new domain in alongside your existing domain. This means things like the exchangeservers.txt file etc. Then you can use the Deployment Scanner to point you in the right direction on some things. Though I didn’t really find this any use as this was saying everything was OK though it wasn’t.

On the Vault server, we added the exchange Targets for the new mail servers. Also added the tasks for archiving and provisioning. I had some issues with getting this all working but my problems were based around MAPI issues. Basically, from this box we were unable to use Outlook to connect to the new mail server – this was more of an outlook issue.
I had to regedit, HKCU \ Software \ Microsoft \ Exchange \ Exchange Provider. Within this I had two options which I needed to delete. 1) Use closest GC 2) Something about a DS server - which was pointing to the old domain.I deleted both of these and restarted the Vault server and then I was all ok.

From memory, a big stumbling block was getting the vault.anon (ev.anon) user working on both domains. But again this was actually pretty simple. As we are keeping the Vault server on the old domain during the migration we use the old domains Vault.Anon user on the new domain.
To do this we just needed to grant it it’s required rights in Exchange System manager – this is standard stuff but we are using the old domain user on the new domain. Again, same as usual, you don’t want to add domain admin rights for the vault.anon user or send on behalf of rights get messed up.

Just like a normal new setup, I needed to setup the provisioning group policies for the new domains and its OUs. This was just copied from our old domain policies and assigned to the relevant OUs in the new domain.

The Exchange servers needed setting up for Vault, vault installing and the OWA scripts running on FE / BE servers. Just like a normal new install. Remembering to have the vault names in the text files for the setup script to pickup. All standard stuff here.

Then before you start the migration, you need to set the syncinmigrationmode reg key to 1 on the Vault server.
FYI HKLM\SOFTWARE\KVS\Enterprise Vault\Agents\SynchInMigrationMode
0 = warn in event log only
1 = link mailboxes (good for this kind of migration)
2 = start a new vault mailbox / users will end up with 2

After that, various reboots and reruns of provisioning tasks we were ready to go.

The first user was an epic fail. The second was much better though, with the user being able to see his vaulted items and after a rerun and resync of the provisioning task, the user was able to vault items and the scheduled vaults were happening according to policy.

To fix the first user it was down to SQL changes. I logged on to the SQL box and did the following for the broken user:
Look at how many records a user has, In this example using SLACK as the user:
USE EnterpriseVaultDirectory
SELECT *
FROM ExchangeMailboxEntry
WHERE (LegacyMbxDN LIKE '%Slack%')order by MbxAlias

This showed the broken user with a few records appearing, so we just needed to delete them.

delete the user

USE EnterpriseVaultDirectory
DELETE
FROM ExchangeMailboxEntry
WHERE (LegacyMbxDN LIKE '%Slack%')

So for the broken users I am now fixed.

Basically, you just need to keep with it and use the event log and the help files a lot. If you are proficient in Vault this would be a really easy process. For those who aren’t like me, it can be one problem after another but it does work.

I will get this post tidied up at some point but for now I hope this helps.