Rated 4 out of 5 stars
Tomas, is your software open source or not? It seems like you are saying that it is open source, but that you are asking us nicely not to use it in an open source way? That is no modifications, derivative works or distribution without your permission? Perhaps you should adopt one of the well-known lisences so that folks know what their rights are? See below for the contradiction in your intro on http://sieve.mozdev.org/
"This software is open source, but it remains my intellectual property. Therefore please ask before you modify or use the code for other projects. It is Freeware, this means it is not allowed to sell it and therefore it can't be bought by anyone. "
Thanks for the software (I am ecstatic that someone is writing a sieve add-on for thunderbird!) , but please clarify what your user's rights are (whether the software is free as in freedom, or whether it is proprietary freeware).