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Original KB number: 3002659
Symptoms
When you create a mail contact by using the Exchange admin center in Exchange Online, you receive an error message that resembles the following:
Error
The length of the property is too long. The maximum length is 64 and the length of the value provided is 67.
Cause
This problem occurs if an existing contact (the DisplayName parameter) or an existing external contact (the ExternalEmailAddress parameter) has the same name that you try to use for the new mail contact.
Resolution
Give the new contact a name that doesn't conflict with an existing mail contact or an existing external contact.
More information
The error message that's described in the Symptoms section is not the correct error message for the scenario. This is a known issue in Microsoft 365. You receive the correct error message if you try to create a duplicate contact by using Exchange Online PowerShell.
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