There is no support for identities for EWS accounts right now -- because I just don't know how to set them up server side and how they're supposed to work.
If you can clarify that, I can look into it.
I do have an Exchange Online account for tests (Office 365 without Office).
This is how to set up alternative "send from" accounts in Office365. They are known as "Connected Accounts" and further information can be found at the following URL (sorry, it won't let me post a proper URL):
community.office365.com/en-us/blogs/office_365_community_blog/archive/2011/06/09/getting-start-with-connected-accounts.aspx.
(That article is a couple of years old and says that connected account mailboxes are polled hourly. That has since improved and in my experience they seem to be polled every 10 minutes).
My short description of how to set them up is:
- Go to the Outlook tab in Office365's web interface.
- Click the settings cog wheel and then click Options.
- In Account settings you should see "my account" and "connected accounts". Click "connected accounts".
- Click "+" to add a connected account and it will ask for email address. passwords etc and test that it can connect to the mailbox.
- From memory, I think it also takes you through some sort of validation to ensure that access is authorised. Once you've done that
- you can use the connected account's email address to send emails from.
HTH. Let me know if you need any more info. I'd be very glad to help out by testing etc if you like.
