sieve - find in header

Hello list,

have a problem with sieve script. I want to perform an action if an arbitrary headerline contains a defined string. I tried with regex:

if header :regex [".*"] ["searchstri.*"] { fileinto "junk"; }

This is not working because regex is only used in 2nd argument ["searchstri.*"] In 1st argument [".*"] no regex is used, sieve expects just plain string. Something like this would work, if "x-myheader" contains "searchstring": if header :regex ["x-myheader"] ["searchstri.*"]....

How to solve this case and find a string in arbitrary/unknown headerline?

Thanks, Hajo