Microsoft Outlook - Uwe Gradenegger

Microsoft Outlook: Signed e-mail messages are rejected by the receiving mail server with error message "Invalid S/MIME encrypted message."

Assume the following scenario:

A user sends an e-mail message signed with Secure/Multipurpose Internet Mail Extensions (S/MIME).
The sender uses Microsoft Outlook for Macintosh.
The receiving mail server rejects the message and sends back a Non-Delivery Report (NDR):

550 5.6.0 M2MCVT.StorageError.Exception: ConversionFailedException - , Content conversion: Invalid S/MIME encrypted message.; storage error in content conversion.

Microsoft Outlook: Signed e-mail messages appear invalid with error message "No certificate was found to verify the signature of this message."

Assume the following scenario

A user receives an e-mail message signed with Secure/Multipurpose Internet Mail Extensions (S/MIME).
The user (the recipient) uses Microsoft Outlook for Windows.
The sender uses Microsoft Outlook for Macintosh.
The certificate used to sign the message is valid.
The e-mail signature is displayed as invalid. Inspection of the signature reveals that no details about the signature certificate can be displayed.

Error: No certificate was found to verify the signature of this message.
Signed by (certificate subject name unknown) using RSA/SHA256 at 15:44:59 19.05.2021.

Microsoft Outlook: "This message cannot be encrypted or signed by Microsoft Outlook because there are no certificates for sending messages from the email address [...]."

Assume the following scenario:

A user wants to send a signed e-mail
The operation fails with the following error message:

This message cannot be encrypted or signed by Microsoft Outlook because there are no certificates for sending messages from the email address "rudi.ratlos@adcslabor.de". Either request a new digital ID for this account, or use the Accounts button to send the message using an account for which you have certificates.

Microsoft Outlook: Emails encrypted with S/MIME cannot be opened. The error message "Internal error." appears.

Assume the following scenario:

A user receives an e-mail message encrypted with Secure/Multipurpose Internet Mail Extensions (S/MIME).
The message cannot be opened.
When opening the message, the following error message is displayed:

Unfortunately, there is a problem opening this item. This may be temporary. If this error occurs again, you should restart Outlook. Error in the underlying security system. Internal error.

Microsoft Outlook: Find out recipient certificates for S/MIME encrypted mails

For troubleshooting e-mail messages encrypted using Secure/Multipurpose Internet Mail Extensions (S/MIME), the encrypted part of a message can be exported. See article "Microsoft Outlook: Extracting an encrypted S/MIME message from an email„.

To find out with which certificates a message has been encrypted, you can proceed as follows...

Microsoft Outlook: Extracting an encrypted S/MIME message from an email

The encrypted part of an e-mail message encrypted with Secure/Multipurpose Internet Mail Extensions (S/MIME) is always contained in a file called "smime.p7m" as an attachment to the mail.

Outlook does not display this attachment, but it can be analyzed using the free Microsoft MFCMAPI extracted from the e-mail.

Microsoft Outlook: Emails encrypted with S/MIME cannot be opened. The error message "Your digital ID name cannot be found by the underlying security system" appears.

Assume the following scenario:

A user receives an e-mail message encrypted with Secure/Multipurpose Internet Mail Extensions (S/MIME).
The message cannot be opened.
When opening the message, the following error message is displayed:

Sorry, we're having trouble opening this item. This could be temporary, but if you see it again you might want to restart Outlook. Your digital ID name cannot be found by the underlying security system.

Microsoft Outlook: Correctly signed e-mails (S/MIME) are displayed as invalid after the signature certificate expires

Assume the following scenario:

A user has received an email message in the past.
The message was signed with an S/MIME certificate.
The sender's signature certificate was issued by a certification authority that has been granted trust status with the recipient.
Thus, the signature was recognized as valid at the time the message was received.
The user opens the mail again some time later and finds that the signature is classified as invalid.

Microsoft Outlook: View which algorithm was used for an S/MIME encrypted or signed email

Below is a description of where it is possible to view which symmetric algorithm was used to encrypt an email received, and which hash algorithm was used for a signed email.

Microsoft Outlook: Control the encryption algorithm used for S/MIME.

When S/MIME certificates are issued, they usually contain a certificate extension "S/MIME Capabilities". This certificate extension is specified in RFC 4262 and can be used by compatible e-mail programs to specify the symmetric algorithms supported by the recipient of an encrypted message. The sender should then choose the strongest algorithm supported by the recipient.

Microsoft Outlook uses (if available and required) the information in the "S/MIME Capabilities" extension of a certificate. Below is a description of how it is used and which algorithms are selected.