We have seen that some servers after some time fail to allocate handlers for objects that are responsible for parsing the RTF (there is a similar and less common issue with HTML).
To resolve this issue, we make SIP filter makes 2 parsing attempts and if both fail we send the content without parsing - AS-IS.
Here are the logs that document the process:
WARN DLP: failed with parising parsing RTF: Error creating window handle. [failed in the first attempt]
WARN DLP: try different method [going to try a different way]
WARN DLP: failed with parising parsing RTF in the second time: Cannot create a file when that file already exists [failed in the second attempt]
WARN DLP: inspect all content AS-IS [content sent to DLP without parsing]