Spare* source channel options

Extra value channel options: (string)
The   source channel options provide functionality (  = 1,...,18) are analogous to the attributes named by the     MTA options, except with these options the corresponding spare slot is filled in when the source channel is selected.

The spare value slots are intended for site-customizable purposes, to be made known to the MTA (and hence be more easily accessible in MTA LDAP URLs and certain MTA mapping tables, etc.).

See also:
 * Channel options
 * alias_spare1 Option
 * ldap_spare_1 MTA Option