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RFC 2369 / MAILING LIST COMMANDS

Read bracketed alternatives without losing boundaries

02

A field contains angle-bracketed URLs, optionally separated by commas and surrounding comments or white space.

DIAGRAMRead RFC section 2 ↗
RFC 2369 · § 2EXAMPLE
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Read bracketed alternatives without losing boundariesFive parsing cases. Two bracketed URLs separated by an outside comma produce two alternatives. Receiver tolerance removes an inserted internal space without permitting generators to insert it. A bare non-angle start is ignored. Non-comma trailing text is ignored while the first URL remains. After a comma introduces an unbracketed item, that item and the remainder are ignored, including a later valid-looking URL. These are separate examples and parsing decisions, not executed commands. The bounded model handles only the illustrated unfolded ASCII cases.Read boundaries before choosing an action<mailto:help@example.org>,bare,resume at a later URL<https://example.org/later>Ignore malformed item + remainderFirst URL remains: 1 parsed alternative
05
Stop at a malformed alternative.

After a valid first URL, a comma introduces an unbracketed sub-item, followed by a later valid-looking URL. The malformed item and remainder SHOULD be ignored; the already parsed first URL is not retroactively erased.

Source for this drawing: RFC 2369 · Read RFC section 2 ↗

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KEY POINT

A comma separates alternatives only outside an enclosed URL.

  • MTAs (mail transfer agents) MUST NOT insert whitespace inside the brackets. Client applications should ignore any such inserted whitespace; this is receiver tolerance, not generation permission.
  • A client MUST follow the §2 handling guidelines: except for field-specific exceptions, a non-angle beginning SHOULD cause the field to be ignored; trailing characters SHOULD be ignored unless the next non-whitespace/comment character is a comma.
  • If a comma-separated sub-item is not an angle-bracketed URL, that item and all later items SHOULD be ignored. Do not skip a malformed item and resume with a later command.
DETAILS

The examples use unfolded ASCII field bodies, not whole raw mail. Comments and URL values have different boundaries. No URL is fetched. The bounded teaching parser does not implement all RFC822 folding/encoding or all URL syntax; its size/depth guards are local model limits, not RFC2369 mandates.

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