Bangoverpercent, nobangoverpercent, bangonly, percentonly, nobangorpercent Channel Options

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Interpretation of local parts (bangoverpercent, nobangoverpercent, bangonly, percentonly, nobangorpercent)

The local parts of addresses are interpreted in accordance with the rules specified in RFC 5322 and RFC 976. However, there may be occasions when interpretation of embedded routing information is inappropriate. Additionally, ambiguities in the treatment of certain composite addresses that are not addressed by these standards. In particular, the interpretation of exclamation points and percent signs appearing in the local parts of addresses in domains the MTA has administrative authority over are not specified in any standard. These characters are sometimes used to provide a form of explicit multihop routing comparable to source routes.

Several source channel options are provided to control the interpretation of these characters. nobangorpercent disables special interpretation of both characters completely. bangonly treats local parts of the form A!B as a route from routing host A to user B; percent signs have no special meaning. percentonly treats local parts of the form A%B as a route from routing host B to user A; exclamation points have no special meaning.

If both characters are used to specify routing a question arises as to which one has precedence. 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.

In any case, the bangoverpercent channe; option forces the former A!(B%C) interpretation. nobangoverpercent forces the latter (A!B)%C interpretation. nobangoverpercent is the default for all channels.

See also: