Gettting error while sending S/MIME mail using Outlook on web

Question

Hi all,

I have a Microsoft 365 account with an Exchange Online license. I am sending a mail using S/MIME I am getting the below errors:

After getting this error I created a S/MIME certificate using OpenSSL in the following document: https://johndalesandro.com/blog/create-self-signed-smime-certificates/

and configured the certificate using a Microsoft document: https://support.microsoft.com/en-us/office/encrypt-messages-by-using-s-mime-in-outlook-on-the-web-878c79fc-7088-4b39-966f-14512658f480

But getting an error while sending mail :

Questions:

1. Can you provide me Prerequisites I have to follow for sending S/MIME mail?
2. How can I create a S/MIME certificate set on Outlook on the web?

Answer 1

Dear Vinay Sharma

Welcome to Microsoft Q&A Community.

Please refer the following information:

Questions:

1. Can you provide me Prerequisites I have to follow for sending S/MIME mail?

The document you provided is correct, you also could refer to Encrypt messages by using S/MIME in Outlook Web App - Microsoft Support which is similar to yours.

1. How can I create a S/MIME certificate set on Outlook on the web?

I’m afraid not.  From“ The first step to use S/MIME is to obtain a certificate, also called a digital ID, from your organization’s administrator.”  We could know that the administrator should provided the certificate. For admin task, we could refer to S/MIME for message signing and encryption in Exchange Server | Microsoft Learn