Native FileMaker script step send email does so on a "mailto" command to the OS. The OS then determines the default mail application such as Outlook, and opens it up and creates a new email. The process natively does not include options or variables for selecting a mail applications options or templates other than the usual options such as BODY, SUBJECT, TO, CC, BCC, and one attachment.
If this is really important to have an elegant solution, you could use a plugin like ScriptMaster and program with Groovy language to do exactly what you want, but this is not a trivial process. If you're interested, you should check with the 360Works people in Atlanta. They make ScriptMaster and can do the Groovy programming for you if you will pay for it.
There are a number of FileMaker plugins that let you use HTML formatting to send emails. You could develop your own HTML template and use one of these plugins more easily than the ScriptMaster solution. But it won't be an exact template of what you have in Outlook.
My suggestion is to look into HTML emails. ScriptMaster is a free plugin and allows HTML emails. But if you don't mind paying for it, I like the CNS SMTPit plugin for sending HTML emails.
I will indeed look into HTML emails as this sounds like it could be the solution for me..
Thank you so much for your help!