When PureMessage is installed on an Exchange 2013 Client Access (CAS) Server, EML files are written to the root of the system drive, by default this is C:\.
A typical file has the below properties:
PureMessage trigger message sent by MailSending.dll
First seen in
PureMessage for Microsoft Exchange 4.0
Client Access Servers do not have the Exchange Replay directory which is required by PureMessage.
What To Do
PureMessage is not supported on Exchange 2013 Client Access (CAS) servers and must be uninstalled. The PureMessage startup guide will be updated to include this information.