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Microsoft 365 tenant-to-tenant error

Duplicate proxy addresses (Exchange Online licence fails)

Assigning an Exchange Online licence fails because another object already has the same proxy address.

Checked 4 Nov 2026Official source linked
Duplicate proxy addresses (Exchange Online licence fails)

Assigning an Exchange Online licence fails because another object already has the same proxy address.

Why it happens

Exchange Online licensing can fail when two users have the same proxy address. In a tenant-to-tenant move, check for addresses copied onto new users before they were removed from the old objects.

How to fix it

  1. 1

    Step 1

    Find which object already holds the address.

  2. 2

    Step 2

    Remove the duplicate address from the wrong object (on-premises if it is synced from AD).

  3. 3

    Step 3

    Reprocess the user or group licence assignment.

Get-Recipient -ResultSize Unlimited | Where-Object { $_.EmailAddresses -match "user@contoso.com" } | Format-List Name, RecipientType, EmailAddresses

Source

Microsoft Learn: Identify and resolve licence assignment problems for a group

Full guide: Microsoft 365 tenant-to-tenant migration: the complete guide →