Reference:
https://docs.microsoft.com/en-us/exchange/email-addresses-and-address-books/email-address-policies/email-address-policies?view=exchserver-2019 Email address policies define the rules that create email addresses for recipients in your Exchange organization.
The basic components of an email address policy are:
Email address templates: Define the email address format for the recipients (for example <firstname>@contoso.com or <lastname>.<firstname>@contoso.com).
Recipient filter: Specifies the recipients whose email addresses are configured by the policy.
Priority: Specifies the order to apply the email address policies (important if a recipient is identified by more than one policy).
The EmailAddressPolicyEnabled parameter specifies whether to apply email address policies to this recipient. Valid values are:
$true: Email address policies are applied to this recipient. This is the default value.
$false: Email address policies aren't applied to this recipient.