+PH/08 The redirect router has two new options, sieve_useraddress and
+ sieve_subaddress. These are passed to a Sieve filter to specify the :user
+ and :subaddress parts of an address. Both options are unset by default.
+ However, when a Sieve filter is run, if sieve_useraddress is unset, the
+ entire original local part (including any prefix or suffix) is used for
+ :user. An unset subaddress is treated as an empty subaddress.