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, or C as the routing host and A as the final destination host.
While RFC 976 implies that it is all right for mailers to interpret addresses using the latter set of conventions, it does not say that such an interpretation is required. In fact, some situations may be better served by the former interpretation.
bangoverpercent keyword forces the former A!(B%C)
nobangoverpercent keyword forces the
latter (A!B)%C interpretation.
nobangoverpercent is the
default. See Section 188.8.131.52 for further details.
This keyword does not affect the treatment of addresses of the form A!B@C. These addresses are always treated as (A!B)@C. Such treatment is mandated by both RFC 822 and RFC 976.