iOS: Issues and resolutions with S/MIME and Exchange 2010

New to iOS 5 is support for S/MIME. Learn how to resolve issues that may occur when using iOS with an Exchange 2010 account.

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1. Signed and encrypted messages sent from Outlook 2010 to iOS do not appear signed

  • First, verify that Outlook 2010 is updated to Service Pack 1 (SP1). If you are not able to apply SP1 to Outlook 2010, please refer to this Knowledge Base article from Microsoft for detailed steps to reconfigure Outlook 2010 for broader encryption-method support.
  • The issue might still manifest itself in the following way:
    The message sends successfully from Outlook and can be read in iOS Mail, but the message does not appear to be signed or encrypted.
S/MIME not enabled S/MIME enabled


Solution: Consult the appropriate device User Guide for iOS (iPad, iPhone, iPod touch) to learn how to enable S/MIME for the Exchange 2010 account configured on the device.

2. Signed and encrypted message replies and forwards sent by iOS do not appear signed and encrypted

  • Outlook 2010: The message will be readable but will not appear signed or encrypted.
  • iOS Mail: The message will be readable, but will not appear signed or encrypted. The message will have an attachment named "smime.p7m".
Example reply message Example forwarded message


The smime.p7m attachment can be viewed in TextEdit. In both the reply and forward cases, the .p7m file contains content-boundary-definition information, a text rendition of the message, an HTML rendition of the message in some cases, and the base-64-encoded digital signature.

Solution: Update to iOS 5.1 or later.

3. Signed messages sent by iOS do not appear signed

When sending a signed, unencrypted message that is not a reply or a forward using iOS through an Exchange 2010 server, recipients may find that the message signature is invalid.

Solution: A simple workaround is to append one or two carriage returns to the end of the signed message body before sending the message. This issue is addressed by Exchange 2010 SP1 RU3 or later.

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