Jooel, I've been testing with this ini:

 Code:
[Test 1]
Blocksize=5
Permutation=3,5,2,1,4
Input =Collegiate Programming Contest
Output=leoClaeigt orrPgmnmaio tCgntse
[test 2]
Blocksize=5
Permutation=3,5,2,1,4
Input =G, ,B
Output=B, ,G
[Test 3]
Blocksize=5
Permutation=3,5,2,1,4
Input ="ACM"
Output="MCA"
[Test 4]
Blocksize=5
Permutation=3,5,2,1,4
Input =Springfield, MA
Output=rnpSiilfgeA, Md
[Test 5]
Blocksize=5
Permutation=5,3,4,2,1
Input =Springfield, MA
Output=nripSliefgA, Md
[Test 6]
Blocksize=10
Permutation=3,5,2,1,4,6,10,9,8,7
Input =This is a very long text, something I hope will work
Output=iihT ss r evao glyn tstx, eehmotihI g neip owlr owlk


It's got a different permutation in Test 5 and a Block length = 10 in Test 6.

In the rules message is the text:
 Quote:

Note that blanks and punctuations are not counted in any block, and should be left in their original positions. Note that the last block should be handled differently if it does not contain the full length of characters. In the example, the last block is "est". Since it contains only 3 characters, we eliminate 4 and 5 from the permutation "3 5 2 1 4" and use "3 2 1" to reorder the last block and get "tse".

1 <= Blocksize <= 10
Characters are a-z and A-Z


and later on Jens says:
 Quote:

Anything that is not a letter or number would fall under the "punctuation" category.


This means that any character other than a letter is considered a punctuation.

That's also why I'm not sure if a number is a valid character in the message body...
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The Code is out there