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RFC 2919 / MAILING LIST IDENTIFICATION

Compare identifiers and preserve list continuity

03

List identifiers have one defined operation: case-insensitive equality. Delivery hosts and display names can change without changing the list key.

DIAGRAMRead RFC section 6 ↗
RFC 2919 · § 6EXAMPLE
4 / 4
Compare identifiers and preserve list continuityFour comparisons. Garden Notes with Garden.Example.ORG and Weekly Garden with garden.example.org compare equal after ASCII case folding and ignoring the descriptions. Delivery then moves from old.example.net to new.example.net while the key remains garden.example.org. A changed key seedlings.example.org compares different and SHOULD be treated as another list. Finally an intentional unmanaged-to-authorized-domain migration is permitted but changes identity; no automatic alias or filter migration is defined.A deliberate migration may change identityExisting .localhost identifieradministrator MAY changegarden.example.orgAuthorized-domain transition is acceptableNo automatic alias discovery defined
04
Allow deliberate migration.

An administrator MAY move an unmanaged .localhost list into its authorized domain namespace. That changes the identifier; this RFC does not define automatic alias discovery or filter migration.

Source for this drawing: RFC 2919 · Read RFC section 6 ↗

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KEY POINT

Compare only inside the brackets, ignoring case.

  • Comparison MUST ignore everything outside the angle brackets. Case changes inside the identifier do not create a different list.
  • Administrators SHOULD avoid changing an identifier even when the delivery host changes. They MAY change it; clients SHOULD treat a different identifier as a different list.
  • An unmanaged-to-domain transition is an acceptable reason to change the ID. A description change has no identity cost; a client MAY notify the user about it.
DETAILS

The stable key can drive an inbox filter, but not automatic trust. These fictional comparisons show ASCII case folding; they do not add aliasing, DNS canonicalization or equivalence between different IDs.

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