Do archive first, then auto-expand. Auto-expand only works in Exchange Online PowerShell (not the EAC). Microsoft: enable archive · Microsoft: auto-expanding
Auto-expanding cannot be turned off after it is on, and it affects inactive mailbox recovery. Read Microsoft’s “before you enable” notes before running org-wide.
1. Enable Online Archive
EAC: Recipients → Mailboxes → user → Others → Manage mailbox archive → on → Save. Wait until Archive status is Active.
PowerShell (one user):
Enable-Mailbox -Identity 'user@domain.com' -Archive
2. (Optional) Auto-create archive when primary hits ~90% full
Org-wide. Still needs a license that includes archiving.
Set-OrganizationConfig -AutoEnableArchiveMailbox $true
3. Enable auto-expanding archive
Whole tenant:
Set-OrganizationConfig -AutoExpandingArchive
One mailbox (archive must already be enabled):
Enable-Mailbox -Identity 'user@domain.com' -AutoExpandingArchive
Hybrid: primary on-prem + archive in cloud → use only org-wide Set-OrganizationConfig -AutoExpandingArchive for those users, not per-mailbox Enable-Mailbox -AutoExpandingArchive.
4. Check
Get-OrganizationConfig | Format-List AutoExpandingArchiveEnabled, AutoEnableArchiveMailbox
Get-Mailbox -Identity 'user@domain.com' | Format-List Archive*, AutoExpandingArchiveEnabled
Extra archive space often appears in stages; Microsoft cites up to ~30 days after the archive is large enough (~90 GB including Recoverable Items).