Dynamics 365 Email Template for Custom Entity

 Use the following syntax to insert fields from custom entities

Field Type	Syntax
Single line of text Currency Multiple lines of text Decimal number Floating number	{!EntityLogicalName:FieldLogicalName;}
Lookup Multi-select option set Option set	{!EntityLogicalName:FieldLogicalName/@name;}
Date	{!EntityLogicalName:FieldLogicalName/@date;}
Time	{!EntityLogicalName:FieldLogicalName/@time;}

 

More info can be found at: 

https://learn.microsoft.com/en-us/power-apps/user/email-dynamic-text