I would like to know if it is possible to open and reply as a response message on top of a saved .eml file using C#?
If yes, are there any guides that I can follow?
I am able to do so with EWS EmailMessage where the message resides in Inbox. However, due to requirements, I am required to retrieve and reply from a saved .eml file instead of replying from the email in Inbox directly.
Thank you.
No you can't do this using the EWS reply operations because EWS is a Server side API while using the EWS Managed API you using Client side library that just instrumenting the SOAP call to the backend whenever an action is taken. You can temporary import the EML back in the server https://learn.microsoft.com/en-us/exchange/client-developer/exchange-web-services/how-to-import-items-by-using-ews-in-exchange and then you reply and then delete the Message again if don't want it to exist. If your want to send using EWS you didn't want to import the message use something like mimekit to generate the MIME of the response message offline http://www.mimekit.net/docs/html/Frequently-Asked-Questions.htm then you can just sent the Mime generated by mimekit via EWS.