Your Digital ID name cannot be found by the underlying security system
Beginning with Outlook build 16.0.8518.1000, Microsoft upgraded the default fallback algorithm from 3DES to AES256. So, when the user using Outlook 16.0.0.8518.1000 or later sends the encrypted email message and you try to open it by using a certificate that has only 3DES encryption capabilities, you see the error message. The error can be temporary but if it continues to persist you may try fixing it by following the instructions given below. Press Win+R in combination to open the RUN dialog box. In the empty field of the box type Regedit and hit Enter. When the Registry Editor opens, navigate to the following path address – Next, in the right pane, create a new DWORD Value – UseAlternateDefaultEncryptionAlg.
Double-click the entry to edit its value. Change it from default 0 to 1. Similarly, create a new STRING value – DefaultEncryptionAlgOID.
Double-click the entry to edit its value. Enter the following value – 1.2.840.113549.3.7. The provided string value shows the OID for the 3DES encryption algorithm. When done, close the Registry Editor and Exit. Let us know if this helps.
