Add sieve support

Packages describing “sieve” as local USE flag

Package “sieve” Flag Description
net-mail/dovecot Add sieve support
mail-client/claws-mail Build plugin for sieve filter support
net-mail/cyrus-imapd Enable sieve support
net-mail/dbmail Enable sieve filter support
sci-mathematics/yafu Use msieve for the sieving steps of NFS

All packages providing a “sieve” USE flag (4)