c# - EWS: Retrieving attachments from signed emails

Question

I have a C# program that manages a resource mailbox by retrieving attachments and categorizing emails into sub-folders. An issue came up recently where the client wishes to send us signed emails, so when the program retrieves their attachments a file named "smime.p7m" is saved instead of the file attachments. This file is not present when reviewing the email in Outlook, only the attachments we want. However, when stepping through the code, the attachments listed in the Email object only contains this .p7m file.

I have retrieved the mime content from the email, but it's just bytes. When I look at the .p7m file in a text editor, I see the contents of the file(s) I want at the bottom file (the ultimate tease)! How do I get the original attachments without having to parse the .p7m file for the content of interest?

The exchange server is 2010 SP2, and this is all happening via a C# program utilizing the EWS Managed API.

Answer 1

You should check out MimeKit (MIME parser + S/MIME and PGP support) and MailKit (if you need SMTP, POP3, and/or IMAP).

I've written some examples on how to use MimeKit's decryption and signature verification APIs in the documentation on the main page of the GitHub project.