Minimal PSTN address format in Internet Mail
obsoleted by
- rfc-3191 — Minimal GSTN address format in Internet Mail
Extracted elements (19)
The optional '/' characters in pstn-email result from compatibility with other mail transport service gateways where '/' is also an optional element; the design preserves interoperability with those systems while discouraging generation of the slashes.
The specification is intentionally minimal: the generic complex case of converting the whole PSTN addressing into e-mail is out of scope, and the standard extension mechanism (qualif-type1) is provided for further standard elements to be defined in service-specific documents.
Written separators ('-' and '.') are allowed in global-phone to facilitate user input of PSTN e-mail addresses by permitting insertion of separators between dial elements, though their use is not recommended and implementations must ignore them.
When multiple subaddresses are needed for the same global-phone, multiple pstn-email elements MUST be used. The UA may accept multiple subaddress elements but MUST generate multiple pstn-mbox elements when passing the message to the MTA.
All implementations supporting PSTN over e-mail service MUST support as a minimum the specification described in this document, including the global-phone syntax.
Any non global-phone dialling schema MUST NOT use the leading '+' between the '=' sign and the dialling string; the '+' sign is strictly reserved for the standard global-phone syntax.
Conforming implementations MUST preserve all qualif-type1 address elements they receive, even if they choose to ignore non-minimal extensions.
Implementations MUST accept the optional leading and trailing slash characters in pstn-email but SHOULD NOT generate them. Gateways are allowed to strip them off when converting to Internet mail addressing.
Specifications adopting the pstn-address definition MUST define a unique case-insensitive service-selector element to identify the specific messaging service involved, and MUST define which minimal qualif-type1 extensions are required.
The pstn-address element MUST strictly follow the quoting rules specified in RFC 822 and RFC 1123.
Written separator elements (written-sep: '-' or '.') in a pstn-mbox MUST be ignored by all conformant implementations. User Agents SHOULD remove written-sep elements before submitting messages to the MTA.
The minimal PSTN address format is defined as 'pstn-address = pstn-mbox [ qualif-type1 ]' where 'pstn-mbox = service-selector "=" global-phone'. The service-selector identifies the specific messaging service (e.g., VOICE, FAX, SMS).
The mta-I-pstn (the e-mail address of the I-pstn device) is the Right Hand Side of the address (domain part after '@'). For SMTP it MUST conform to RFC 821 domain specifications; for message headers it MUST conform to RFC 822 and RFC 1123.
Mail routing based on DNS is vulnerable to attacks including DNS server compromise, counterfeit DNS query responses, and incorrect additional information in unrelated query responses. Clients SHOULD ensure mail routing is based only on authoritative DNS answers.
Once DNS Security mechanisms (DNSSEC, RFC 2065) become more widely deployed, clients SHOULD employ those mechanisms to verify the authenticity and integrity of mail routing records for PSTN e-mail gateway addresses.
The complete pstn-email structure is defined as '['/'] pstn-address ['/'] '@' mta-I-pstn'. The optional '/' characters may appear from other mail transport service gateways.
The global-phone field is defined as '+' followed by 1 or more DIGITs and optional written separators ('-' or '.'). The leading '+' is strictly reserved for the standard global-phone syntax.
The qualif-type1 extension element is encoded as '/ keyword "=" string', where keyword is 1 or more DIGIT/ALPHA/'-' characters and string is printable characters (%x20-7E). All pstn-address extensions MUST use this form.
The service-selector field consists of 1 or more DIGIT, ALPHA, or '-' characters and MUST be handled as case-insensitive. Spaces are not allowed in the service-selector.