We have these and i have term filtered but honestly the most obvious giveaway before you even read it is the font.

I can only think of 1 person who routinely used a different font from Outlook's default in my entire working life. Sometimes you get something copy pasted with formatting from elsewhere but that'll be in the middle of an email.

I dont know why the phishing tests always use a different font.

We only have to do these tests at all because someone bought a load of Apple gift cards for the "CEO".