Good idea - I'd like to implement that. But I need a good idea how to do it technically. Should the default value of the subject when replying already be added with "Re[x]"? Should it be added automatically after posted? What, if someone changes completely the subject line?

Hi Alex,

I guess it should work like this:

- check if the user has renamed the thread
- if yes:
-- make sure he has removed the "Re"
- if no:
-- walk through the thread tree to find the highest RE-Number
-- rename the thread to Re[x]: subject

Regular Expressions might be useful here.
To take subject line and Re-number apart:

$re_no=preg_replace("/^Re:[(d{1,2})]s.+$/","$1",$subject);
$subject_name=preg_replace("/^Re:[d{1,2}]s(.+)$/","$1",$subject);

This is just a sketch of course, not tested yet! I might give it a try myself if if I have the time. Quite probably, some issues might arise I did not think of...

Best

Arnd