add a custom property to a received email

Hi,

Thank you for reading this, I hope you are able to help.

I am trying to add fields to one of my inbox folders in outlook in order to
track the progress of tasks which the emails refer to. Something along the
lines of:
From ¦ Subject (etc.) ¦ Spoken to Joe? ¦ Processed application?

The latter two being yes/no fields which I can put a tick in, thus knowing
where we're up to on any given task. I keep creating custom fields, but I
can't "edit" the qualities in them. I suspect I am using the wrong tool for
the job, but all I want to do is put something (a lot like the follow-up
flags) into the folder.

Input gratefully appreciated