It took me a while to figure out how to do this in Odoo 17 due to the outdated and misleading information available. That's why I want to share the correct method:

Simply use "/" within the body of your Mass Mail, and a new menu will open. Scroll down to the very bottom of the options and select "Dynamic Placeholder." Here, you can choose the value you want to display and optionally add a default value.

That's it. It's quite easy once you know what to do.

To Reference an Object in a mailing template use QWeb tags 

For Name in a Mailing use this placeholder

t t-out="object.name">Name /t

With odoo15 to personalize emails, you should use :

• in subject, expression like : {{ object.name }}
• in mail body, code like :  

 t-out="object.title.name or ''" contenteditable="false" data-oe-t-inline="true">

 t-out="object.lastname or ''" contenteditable="false" data-oe-t-inline="true">

in t xml tag

firstname and lastname are possible fields after installing the OCA module partner_firstname. To insert this code, you have to edit code source of your email (inside html field or with the inspect function of your web navigator) 

Can anyone help how to use company name??

@Dom, you can include just the first name in the mail using ${object.name.split(' ')[0]}

(I can't claim credit for this as I just altered the solution for dates from here (https://www.odoo.com/forum/help-1/question/how-to-change-email-templates-date-format-15885)

hi there, 

is it also possible to just take the first name into the mass mail?

You should use 'object'. This object is a reference to a recipient model. When recipients are customers, try just:

${object.name}

Otherwise, depending on related recipients models. e.g. for leads/opportunities (you may find exact field name in developer mode, while just point on this field):

${object.contact_name}

I have also the same problem.I have checked in developer mode the name of the field and it is "name". I have modified a mass mailing template and used ${object.name} but instead of the customer name, it is {object.name} that appears in the email.  Could anyone help ?

Regards,

Philippe