This post will show you how to quickly create an alternate key. If you want to know more about alternate keys please check out this post.
First you should open your customizations (either default solution or a dedicated solution that contains your customizations) and go to the entity where you want to create an alternate key.
In this post I’ll create an alternate key on contact entity using emailaddress1 field.
Select now one or more available attributes, I selected Email (emailaddres1)
Now you can save and close. A system job creates an index for Email in the database. The status changes from “pending” to “Active”
You can now test your alternate key by creating two contacts with the same email address, while creating the second record you should have the following error