Assume that you are in a Microsoft Exchange Server 2013 or Exchange Server 2016 environment, and then you use an Exchange ActiveSync (EAS) SmartForward or SmartReply command, such as by replying to the message from an iOS client, on a message that contains UTF-8 surrogate pairs, such as emoji. In the sent response, the UTF-8 surrogate pairs in the replied or forwarded message are displayed as question marks.
This issue occurs because when the body is copied to the response message, charset detection incorrectly detects the body as US-ASCII instead of UTF-8, and HTML escaping with US-ASCII conversions does not correctly process surrogate pairs.
To work around this issue, reply to the message by using another protocol or endpoint.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.