Welcome aboard.
Some, but not all, missions do include an
OPTIONAL Enigma message that arrives as part of the email containing the monthly mission theater file. Those who elect to decode it will receive special intel that will not be made available in the regular mission briefing and radio messages.
You can play the mission successfully without the enigma message, but you get a decided advantage if you do (someone may have sighted a particularily nice target or a HK group you'd like to avoid ).
The website has links to download the Enigma software, manual, and code book.