Addresses are always interpreted in accordance with RFC 822 and RFC 976. However, there are ambiguities in the treatment of certain composite addresses that are not addressed by these standards. In particular, an address of the form A!B%C can be interpreted as either:
A as the routing host and C as the final destination host
C as the routing host and A as the final destination host
While RFC 976 implies that mailers can interpret addresses using the latter set of conventions, it does not say that such an interpretation is required. Some situations may be better served by the former interpretation.
The percentonly keyword ignores bang paths. When this keyword is set, percents are interpreted for routing.