Hello, I'd like to know if there's a way to personalize the mass mailing emails.

I need to start the email with 'Dear <firstname lastname>' in the beginning of the email Body. In general I know that you can personalize the emails generated from applications, such as leads and opportunities, as you can use something like 

Dear ${object.partner_id.name}

But in mass mailing it doesn't work like that, because the Recipients field is a selection of other objects.

So can anyone give me a hint of how to achieve the same concept in mass mailing?