Sometimes a transmission method defined by default for the partner is
not applicable. For example, when the transmission method is e-mail and
the partner's e-mail is not set. This addon allows you to define
substitution rules when an invoice matches certain criteria.

This module can also be used when it is not easy to define the partner's
preference for the transmission method or the partner's preference is
not legally permitted. For example, in some countries, invoices with
payment direct debit method must be sent to the customer by post.
