Okay, I have read through several examples and discussions about digitally
signing an excel workbook/code is not easy. My question deals with a mixture
of Excel and Outlook. I don't need to sign the Excel file, but I do need to
digitally sign the e-mail that is generated from within one of many Excel VBA
macros. I'm not sure if this action requires an additional "Add-in" or other
typically installed component to be "selected" or not.

An alternative would be to simply save the e-mail into the users Draft
folder or similar to allow the user to "forward" the message and apply the
appropriate Digital Signature. In order to meet the requirements posed I can
not first send the e-mail to the user and then let them forward and apply the
digital signature.