A beverage services company with operations either side of the Tasman had two Microsoft 365 tenants. Its Australian accounts were in one, and its New Zealand email, on a New Zealand domain, sat in another. The business asked us to bring the New Zealand accounts into the Australian tenant.
We logged 4.6 hours on the move, in late January 2026.
What was moving
Two New Zealand mailboxes: one person’s and one used for accounts. The accounts user also had files in OneDrive that needed to come across, and the New Zealand domain itself had to move from one tenant to the other.
The business already had Australian accounts for the same people. That raised the first real decision.
Keep them separate or merge them?
We could have poured the New Zealand mail into the existing Australian mailboxes. Instead we created shared mailboxes in the Australian tenant to receive them, so the New Zealand mail stayed separate from the Australian accounts.
That keeps two streams of mail apart that people are used to handling separately, and it avoids mixing years of history into mailboxes that were already in daily use. The people who need them see both in Outlook.
Moving the mail and files
We set up a migration tool with a connection to each tenant, granted it the permissions it needed in both, and created service accounts on each side. Then we:
- mapped each New Zealand mailbox to its new shared mailbox and ran verification checks
- started the full mailbox migration
- assigned Microsoft 365 Business Standard licences to the Australian accounts
- set up a separate project to copy the accounts user’s OneDrive into the Australian tenant
Once the full copy finished, we ran an incremental pass to pick up anything that had arrived in the meantime. Mail keeps landing during a migration, and skipping this step is how messages go missing.
Moving the domain
A domain can only belong to one tenant at a time. We removed it from the New Zealand tenant, added it to the Australian one, and updated the DNS records at the domain’s registrar to verify it. Then we waited for the change to spread.
With the domain in its new home, we switched on DKIM for it, added the DKIM and DMARC records at the registrar, and tested that they worked. The domain now has the same email authentication protections as the rest of the business.
Getting people working again
The last part was the desks and phones. On the main laptop and a second laptop, we removed the old New Zealand accounts from Outlook and restarted it so the new shared mailboxes appeared.
We also changed how much older mail Outlook keeps on each machine, and raised the limit on how large its local mail file can grow, so years of history wouldn’t hit a ceiling. Both people had the accounts added to their phones.
OneDrive for the accounts mailbox was set up on the main laptop. On the second laptop, we showed the user how to use OneDrive in the browser instead, to save storage space. We rang to let the business know the migration was done, and arranged a time to finish adding the accounts to phones.
Where they landed
The New Zealand mailboxes, files and domain now live in the Australian tenant, alongside everything else. There’s one set of accounts, licences and security settings to manage, and the domain has DKIM and DMARC in place.
If you have a second tenant somewhere in your business, list what’s in it: mailboxes, files, domains and who uses each. That list is the start of any plan to bring it in.
If you’d like help working out the order to move things in, get in touch.