Hello @FrankF713 ,
By "custom email," do you mean an email built with HTML in the custom code editor? If so, you may want to follow along with this article on adding personalization to custom code emails, which will include info on inserting contact details for the coding.
If you're referring to using the normal email builder, we have the following articles available regarding personalization / adding contacts' details:
Overview of creating more personalized emails
Adding subject line personalization
Adding greeting tags to emails
Adding contacts' details to emails
... View more
