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X-Exchange-Antispam-Report-Test: UriScan: X-MS-Exchange-Organization-AVStamp-Service: 1.0 X-MS-Exchange-Organization-MessageDirectionality: Incoming X-Spam-Class: HAM - SpamAssassin good - Score=-1 * -0.6 RP_MATCHES_RCVD Envelope sender domain matches handover relay domain X-Key-ID: c2hhd24ucnlhbkB0b3VjaHN0b25lYmgub3JnIGxyYXliYWxsQGFyaXpvbmFzY2hpbGRyZW4ub3JnIDIwMTUtMTEtMjIgMjE6NTY6MzUgMWEwazc5LTAwMDgweC04Sg= Thread-Index: AdElsWFigy0vpzmZQXG+e+LUEWWsdw=Ĭontent-Type: application/pkcs7-mime smime-type=enveloped-data Ĭontent-Disposition: attachment filename="smime.p7m" X-ms-exchange-transport-fromentityheader: Hosted Received: from ( )īy with ESMTP id tAN5uW7G026931 Received: from ( helo=) helo=īy with esmtps (TLSv1:DHE-RSA-AES256-SHA:256) Signed) header.d=none dmarc=none action=none SMTP Server (TLS) id 15.1.331.20 via Mailbox Transport Mon, To configure S/MIME for outlook Web App see please refer to this link: (v=exchg.150).aspx As part of our continued investment in security technologies that Government and Security conscious customers care about, we are adding support for S/MIME for Office 365 in the first quarter of Calendar Year 2014. More info :S/MIME – Enables encryption of an email messages and allows for the originator to digitally sign the message to protect the integrity and origin of the message. That's why I sent you the previous link mentioned in my last answer. This issue doesn't look like it was done by a sender but rather something to do with how you retrieve messages from office 365. This could possibly mean that the Outlook communication when pulling messages from office 365 is done in an encrypted way thus creating the behavior you are seeing now.