title: how to display some message once user starts to compose new email
body: <p>For Office 365 Outlook Web App, we would like to convert attachments to links once end user uploads them, however we didn't see an attachment notification event at current Outlook Addin. </p>
  
  <p>Another approach we could do is to ask them to use our own buttons for uploading, however we need to guide end user to use our own buttons, could we add some message at top of email body like below once new email message box is displayed?
  <a href="https://i.stack.imgur.com/LMowc.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/LMowc.png" alt="enter image description here"></a> </p>
  
  <p>Somehow based on our research, Outlook Addin only has one event right now which is <a href="https://docs.microsoft.com/en-us/outlook/add-ins/outlook-on-send-addins" rel="nofollow noreferrer">SendEvent</a>, could someone confirm this? if so, it is rather limited. </p>