Actually now I remember.
Dovecot was bought/merged by open xchange in 2016 and they have a pro version.
Even the pro 2.3 version had full text search problems ( Heinlein consulting)
No idea about Dovecot pro 3.0
Community version is still 2.3
I doubt even with CV 3.0 there will be a solution for free for this problem.
I will move on to another solution