Link email to multiple records

In our CRM 2016 application, when an email is received, we create a new entity record and attach that email to that new record. Is there a way I can share that email with other entity records too.

Fox example, when the first email comes, it creates a record A1 and attaches that email to A1,  and when second email comes  it creates a record A2 and attaches that second email to A2. But I want to reference the second email in the A1, because that second email is regarding the A1. This I have to do in custom entity. 

Thanks,

SJ