fix: forward List-Unsubscribe headers through SMTP proxy#428
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WalkthroughThe SMTP server now defines the forwarded list headers it supports, normalizes header names, and extracts non-empty values from raw parsed header lines. During Possibly related PRs
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Verify each finding against current code. Fix only still-valid issues, skip the
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Inline comments:
In `@apps/smtp-server/src/server.ts`:
- Around line 43-45: Update the header parsing flow around canonicalHeaderName
to unfold folded header values before storing them in result: replace embedded
CRLF followed by whitespace with a single space, then trim the normalized value
and preserve the existing non-empty check and forwarding behavior.
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📒 Files selected for processing (1)
apps/smtp-server/src/server.ts
| const value = line.slice(colonIndex + 1).trim(); | ||
| if (value.length > 0) { | ||
| result[canonicalHeaderName(key)] = value; |
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🎯 Functional Correctness | 🟠 Major | ⚡ Quick win
🧩 Analysis chain
🏁 Script executed:
#!/bin/bash
set -euo pipefail
printf '\n== server.ts outline ==\n'
ast-grep outline apps/smtp-server/src/server.ts --view expanded || true
printf '\n== searches ==\n'
rg -n "canonicalHeaderName|headerLines|mailparser|List-Unsubscribe|unfold|CRLF|replace\\(/\\\\r\\?\\\\n" apps/smtp-server/src -S || true
printf '\n== targeted snippet ==\n'
sed -n '1,140p' apps/smtp-server/src/server.tsRepository: usesend/useSend
Length of output: 5972
🏁 Script executed:
#!/bin/bash
set -euo pipefail
printf '\n== package refs ==\n'
rg -n '"mailparser"|simpleParser|headerLines' package.json pnpm-lock.yaml package-lock.json yarn.lock apps -S || true
printf '\n== test files under smtp-server ==\n'
fd -t f '.*(test|spec)\.(ts|tsx|js|jsx)$' apps/smtp-server . || true
printf '\n== smtp-server tree ==\n'
fd -t f apps/smtp-server || trueRepository: usesend/useSend
Length of output: 3154
🌐 Web query:
mailparser simpleParser headerLines folded header values line property raw headers unfolding RFC 5322
💡 Result:
In the context of the mailparser library, the headerLines property and RFC 5322 specifications relate to how raw email headers are handled, specifically regarding folding and unfolding [1][2]. RFC 5322 defines header folding as the process of splitting a long header field body into multiple lines by inserting a CRLF (Carriage Return + Line Feed) followed by WSP (white space) [2]. Conversely, unfolding is the process of reversing this to reconstruct the original, single-line header field by removing the CRLF and subsequent white space [2][3]. This ensures that headers can be evaluated without length restrictions [2]. In mailparser, the headerLines event provides access to these raw header segments [1]. When you listen for this event, the library emits an array of objects, where each object contains two properties [1]: - key: The lowercase header name [1]. - line: The raw content of that header line as it appears in the message, including any folding [1]. While mailparser processes these raw lines into a structured Map of decoded header values for easier use (e.g., parsing dates, email addresses, or list headers), the headerLines event exposes the unparsed, potentially folded lines for developers who need to access the raw data exactly as it was received [1]. Top results: [1][2][4]
Citations:
- 1: https://context7.com/nodemailer/mailparser/llms.txt?tokens=10000
- 2: https://www.rfc-editor.org/rfc/rfc5322
- 3: https://www.rfc-editor.org/rfc/rfc5322.txt
- 4: https://github.com/nodemailer/mailparser
🌐 Web query:
site:github.com nodemailer/mailparser headerLines line folded header raw as it appears in the message
💡 Result:
In nodemailer/mailparser, the headerLines property is an array of objects that provides access to the header information, where each object contains the key and the line (the raw, folded header string as it appeared in the original message) [1][2]. When parsing an email, mailparser stores individual header lines in this array [2]. Because the library performs parsing and transformations on headers, headerLines serves as a reliable way to access the original, verbatim header lines, including their folding (multi-line) format [1][2]. If you are using the MailParser class directly, you can access headerLines after the parsing process has begun or finished [1]. As of recent updates, you can also listen for the headerLines event to gain access to these raw lines during the parsing stream [1]. Example usage: const { simpleParser } = require('mailparser'); simpleParser(source).then(parsed => { // Access the raw folded lines via parsed.headerLines parsed.headerLines.forEach(header => { console.log(Key: ${header.key}); console.log(Raw Line: ${header.line}); }); }); Note that mailparser is designed to be a streaming parser [3], and while it provides structured header objects (which are often Maps), the headerLines array is the standard mechanism provided by the library to retrieve the exact, raw, folded header content for further analysis or manual reconstruction [1][2].
Citations:
- 1: Emit a new event "headerLines" to gain access to the raw headers nodemailer/mailparser#364
- 2: simpleParser does not add headers to headers object nodemailer/mailparser#197
- 3: https://github.com/nodemailer/mailparser
Unfold folded List-Unsubscribe header values before forwarding. headerLines preserves raw folding, so .trim() leaves embedded CRLF + WSP intact. Unfold the value before storing it; otherwise valid unsubscribe headers can be forwarded malformed.
🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.
In `@apps/smtp-server/src/server.ts` around lines 43 - 45, Update the header
parsing flow around canonicalHeaderName to unfold folded header values before
storing them in result: replace embedded CRLF followed by whitespace with a
single space, then trim the normalized value and preserve the existing non-empty
check and forwarding behavior.
1 participant
This PR modifies the SMTP proxy to allow
List-UnsubscribeandList-Unsubscribe-Postheaders to forwarded to the useSend API.Mailparser transforms
List-*headers into its own internal list structure and drops them from the headers map, so this reads themheaderLines, splits on:, and trims + canonicalizes the names.I’ve been using useSend for sending all kinds of email, most recently including Listmonk campaigns for the first time. mail-tester.com flagged missing
List-UnsubscribeandList-Unsubscribe-Postheaders as negative score impacts, even though Listmonk adds them. There’s no easy way to use a useSend driver rather than SMTP with Listmonk, so this adjustment at least lets the proxy pass them through.Summary by cubic
Forward
List-UnsubscribeandList-Unsubscribe-Postheaders through the SMTP proxy to the useSend API so unsubscribe metadata is preserved and deliverability scores improve.headerLinesto extract these headers sincemailparsermovesList-*into an internal structure and drops them from the headers map.headersfield sent to/api/v1/emails.Written for commit 71022ba. Summary will update on new commits.
Summary by CodeRabbit
List-UnsubscribeandList-Unsubscribe-Postheaders when forwarding outgoing emails.