Thanks, however if I am sending an email to someone called Mark Van Dyke and Peter Michael Smith - if I want to say Dear Last Name, how will Odoo know whether to say Dear Mr Van Dyke vs Dear Mr Smith?

Hi,
In Odoo, there is no strict separation of first name and last name by default. The Name field is often a single field where you enter the full name of a person (first name + last name together). When people have two-word last names, Odoo treats the full content of the Name field as a single value.

Name is the primary full name field used to store the full name of the contact or company.

Complete Name often including parent company names

Thanks