From the Outlook for Mac forum on Microsoft Answers:
From a little time, I have this problem. Some messages are with strange characters. Here an example, but sometimes a messages contains a lot of characters like that. The word is HCI and then there is a S with an accent !!!
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Continue Reading: Avoid strange characters when sending mail through Exchange or Office 365
Microsoft has released the out-of-band Microsoft Office for Mac 2011 14.2.4 Update. (111 MB) Although this update includes prior updates since 14.1.0, installation issues require first installing the 14.2.3 update on Mac OS X 10.7 (Lion) and OS X 10.8 (Mountain Lion) systems due to GateKeeper.
According to the update’s description it adds support for MacBook Pros with Retina displays and includes new features and fixes for Outlook for Mac.
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Continue Reading: Microsoft releases Office for Mac 2011 14.2.4 Update