sieve filter files content order / sieve filter management issue

Issue:

adding new mail filters through remote user (or presumably directly in ispconfig cp, however we didn't test the latter yet) puts the new filter at the top of the users' sieve script. Same happens regarding activating the automatic "move spam to junk folder" filter. Unfortunately sieve requires all require statements at the top of the file.

When using a custom filter with a require statement (in our case it's require "envelope"; ), current behaviour leads to the sieve compiler failing, hence disabling all filters.

Solution proposal:

Add new filter snippets behind the custom filter content or at the end of the sieve file instead, keeping the custom filter content at the top right behind the default require statement.

Alternate solution proposal: Make initial require statement editable

That way one could add more complicated custom rules and keep the user able to add standard filters without breaking mail filtering.