Explanation
Email address policies define the rules that create email addresses for recipients in your Exchange organization whether this is Exchange on-premise or Exchange online.
You can configure email address policies using the graphical interface of the Exchange Admin Center or by using PowerShell with the Set-EmailAddressPolicy cmdlet.
The Set-EmailAddressPolicy cmdlet is used to modify an email address policy. The Update-EmailAddressPolicy cmdlet is used to apply an email address policy to users.
Reference:
https://docs.microsoft.com/en-us/exchange/email-addresses-and-address-books/email-address-policies/email-add