Rewrite rules can possibly act only in conjunction with specific source channels.
When it appears in a message arriving on one channel 2. When it appears in a message arriving on a different channel Source channel-specific rewriting is associated with the channel program in use and the channel keywords rules and norules. If norules is specified on the channel associated with an IMTA component that is doing the rewriting, no channel-specific rewrite checking is done. If rules is specified on the channel, then channel-specific rule checks are enforced. Source channel-specific rewriting is not associated with the channel that matches a given address.