dovecot 2.3.11.3 (that is currently packaged for both f32 and master) supports zstd (to compress mbox) and it's good to have it enabled. To enable it you need to add libzstd-devel to BuildRequires and --with-zstd to %configure
Enabled in git, but as a current latest dovecot release has several issues related to zstd (see thread "zlib errors after upgrading to 2.3.11.3" on dovecot mailing list), I will build and release dovecot package when dovecot 2.3.12 is out.
should be available since 2.3.13-1