I still haven't managed to get rid of the run time error code '287' in our work's Office 2016 setup. It's really annoying as the updated version provided by Graham in post #2 (sorted the signature part) works great at home on my Office 2019 setup.

Just to recap, I've ensured that the object references are identical and Outlook is the default (only) email client at work. Desperate to get this one going.