I find it critical, if a security feature like mail encryption is not working properly, even worse, it seems as mails marked for encryption are sent unencrypted and are only not displayed if the recipient is using outlook as well.
#Decrypt outlook email 2017 update
It seems as if this error occurred first time after the last Win10 Update (2017-05 Update für Windows 10 Version 1607 for 圆4-based systems (KB3150513)) I already tried the online repair function - no success. Luckly, most users nether change the default html format to the plain text, but some advanced do. However, I tried it anyway, deleting the public certificate in the recipients contact information and reinstalling it. We use encripted email then sending a sensitive information in the organisation, and to contractors, and shifting from Outlook 2010/2013 to 2016. It is not a certificate problem, as everything works OK when sending mails in safe-mode. It seems, as the encryption functionality in Outlook 2016 is no longer working.Signing messages is OK Using Outlook 2016 in safe mode, sending and encryption is OK - The reason why this worked was, that in safe mode mails are formatted in html, where in normal mode, I have set up outlook to send mails as plain text, see "Update 2" below.
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I'm using a Win10 圆4 system with Office 2016 Business, version 1704 (last update).