Outlook Web Addin - Need to set Custom Properties in Compose Mode without using Task Pane
I am working on a feature in outlook web add-in where I need to set one custom property in Compose mode without using task pane this will mark and differentiate my email. Same value I will read in On Send event and based on the value I will take decision. I have tried so many ways to achieve that and not able to set custom property. Any help would be great.