New
"Attn. Mr Mayer" belongs in the contact's "Additional info" field. Open the contact, expand the Address and enter the line under Additional info. From then on it appears in the recipient block on every quote and invoice for that customer – no more typing it by hand on each document. The hint next to the field now says so directly.
The Word template guide lists the placeholder. Until now {Address_Line_4} was missing from the ready-made template instructions – anyone who followed them ended up with a template that never printed the address addition. The guide now places it correctly: directly below the recipient name, above the street. If you already have a template, check whether the placeholder is there and add it once if it isn't.