It does.

In your JavaScript console, type "sieveCapabilities" and check the output. You need the "body" extension to appear in the list.

Nice to hear. I have to update my cyrus mail server the next days. May be than it works.

But your JavaScript command doesn't work.

Output in Firefox Javascript console:
ReferenceError: sieveCapabilities is not defined

If I look into the raw generated sieve script from SOGo3. There's only a:
require ["fileinto"];

If I use other sieve editors I get something like:
require ["fileinto","envelope","reject","vacation","imapflags","relational","comparator-i;ascii-numeric","regex","notify"];

It's working now. Thx so much.

I had to add the sieve extension body in /etc/imapd.conf like:
sieve_extensions: fileinto reject vacation ... body ...

Good. For your information, sieveCapabilities is defined on the Preferences pages only:

https://github.com/inverse-inc/sogo/blob/master/UI/Templates/PreferencesUI/UIxPreferences.wox#L23