Microsoft Exchange connection - User Defined field in email

[JemmaD]

I have a connection to a mailbox and within Outlook, users have created a user defined field attributed to each email.

I need to bring this in within Power BI, but I cannot locate it - it doesn't seem to be an attribute. 

If I can find the font size and colour used in the email, I can't believe I can't find a user defined field, does anyone know how I could locate this?

[JemmaD]

No response on this so far... it seems to have something to do with PropertyDefinitionStream which I found under Extended Properties. It seems to be a binary field which I cannot expand due to the format. 

If anyone has been able to get this data I would be really grateful for some guidance.