Graph API cannot get attachments from signed email

Question

When I'm getting attachments for email with electronic signature I receive only 1 attachment - the electronic signature itself.
File name: "smime.p7m"
Content Type: "multipart/signed"

GET https://graph.microsoft.com/v1.0/users/[mailbox]/messages/[resourceId]/attachments

Is it a bug or a feature? Is there a way to overcome it?

Answer 1

@Mark Babayev , Thank you for reaching out. It's not a bug, but its an expected behavior in case of 'multipart/signed' messages.

This format is a clear-signing format.  Recipients without any S/MIME or CMS processing facilities are able to view the message. It makes use of the multipart/signed media type described in [MIME-SECURE]. The multipart/signed media type has two parts. The first part contains the MIME entity that is signed; the second part contains the "detached signature" CMS SignedData object in which the encapContentInfo eContent field is absent.  

More details can be found in the RFC

If the content is signed including any attachments, it gets stored inside the one smime.p7m attachment and it is up to you to extract it.

Hope this helps.

Do let us know if this helps and if there are any more queries around this, please do let us know so that we can help you further. Also, please do not forget to accept the response as Answer; if the above response helped in answering your query