If you use Microsoft Outlook with a Microsoft Exchange Server mail system, you may inadvertently forward a message that other Outlook users cannot open. This symptom occurs when the sender has the Microsoft Exchange message security options enabled and the recipient does not.
Outlook sets the security to match the original message.
This behavior helps prevent someone from inadvertently decreasing the security of an ongoing e-mail thread. This turns off the current security setting. If you do not have the Digitally Sign Message or Seal Message buttons on the message toolbar, then the message you have opened is not signed or sealed. If you do not have these buttons when you compose a new mail message, you are not set up to use these features and cannot open a sealed message. All rights reserved.