HINT 01
You’ll need to have accessed Jess’s mailbox to find the recovered messages.
HINT 02
Look for the time.
HINT 03
Look for abbreviations.
HINT 04
Focus on the words that are only one letter long.
ANSWER
Every letter is replaced with its alphabetic opposite. A=Z, B=Y, C=X etc. and vice versa. So “OK” becomes “LP”, “PM” (mentioned after the time) becomes “KN”, and the word “I” becomes “R”.