> I was rebuilding my mailserver and realized that mail/libsieve does not
> exists ... Is this now part of cyrus...

I don't see libsieve with cyrus. (But it could be.)

Maybe packaging  http://libsieve.sourceforge.net/  would be useful for 
you?

Some mail software provides "sieve" support built-in. What do you use that 
needs a libsieve library?