At de moment we are implement a Email Service in a custom object where we want to received and reply emails but, when we create a EmailMessage register in the Apex class, the register in the chatter component from custom object appear like a task. We want that the EmailMessage register appear like in the Case object.
EmailMessage register in Case object:

EmailMessage register in the custom object:

We want to in the custom object appear the EmailMessage register like in the Case object.
How can we solve it? What are the best prectices?