Dunno if its been mentioned already but frequency analysis is the harder way to recover the key value.
There is a known plaintext attack which works much faster to find the key value.
There are major clues as to what the plaintext for the first 12 characters are, you will find them in the message from the person wanting the stuff decrypted.
Highlight below for one of the clues :
It's an e-mail message ..... so what do e-mails usually start with??
Using the known plaintext, the key value can be found straight away. Assuming the plaintext, work out the key value that recreates the first letter of the plaintext and then apply that to all the other enctypted characters.
There are 10 types of people in the world ... those who understand binary and those that don't.