A superb way of restricting duplicate record creation is using Keys in Dynamics 365CE. This is definitely one of the most useful and easy to use features in Dynamics CRM.
In this example, I will create a Key for Email (emailaddress1) field to ensure there are only unique record values for this fields in my environment.
Create Key
It’s pretty straight-forward like creating any other Dynamics…
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Duplicate Detection in Dynamics 365 using Keys – D365 Demystified
Duplicate Detection in Dynamics 365 using Keys
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