Using SMIME in MS Graph

Question

Hi!

I'm trying to send signed aswell as decrypted E-Mails via MS Graph.

Creating and sending a normal Message is no Problem.
Using S/MIME is mentioned in the Graph API:

• https://learn.microsoft.com/de-de/graph/api/user-post-messages?view=graph-rest-1.0&tabs=http
• https://learn.microsoft.com/de-de/graph/outlook-mail-concept-overview

But how to add a certificate or use S/MIME can't be found.
I've created a signed mime object via openssl and sent this, but the used cert was not added.

Need help please!

Answer 1

You can use SimplaJavaMail: use EmailPopulationBuilder and EMailBuilder to encode subject, body and attachments with your certificate. Than, with EMailConverter you get a MimeMessage. Get a ByteStream out of it, and this one you can send , base64-encoded, with the sendMail-endpoint of the GraphApi.

Unfortunately this only works for attachment-Size < 3MB.

With attachments >= 3MB you have to follow the graph-api doc., see https://learn.microsoft.com/de-de/graph/outlook-large-attachments?tabs=http and https://learn.microsoft.com/de-de/graph/sdks/large-file-upload?tabs=java.

Its unclear how to combine these two approaches.