List-Id header checker: List-Id, List-Help and the other list headers
In short: Paste the headers of a test newsletter. The tool checks the List-Id form and its domain, and the angle-bracket URLs in List-Help, List-Unsubscribe, List-Subscribe, List-Post, List-Owner and List-Archive. Limit: It checks syntax; it cannot tell who owns the domain in a List-Id or whether a link works.
Paste the headers of a test newsletter. The tool checks that List-Id is a description and an angle-bracketed list-label.domain as RFC 2919 writes it, that it sits under your From domain, and that each RFC 2369 list header is a comma-separated set of angle-bracket URLs with no spaces inside, appearing once.
Price: this tool is free. Checking a whole email list is from $9/mo, and the first 100 checks are free with Google, no card. Check your list free nowSee pricing
Sample result
Four list headers read with no problems, and the List-Id sits under the From domain.
- Problems
- 0
- List headers read
- 4
- List-Id
- news.example.org
What this means for you
Each URL header is a comma-separated set of angle-bracket URLs.
- List-Id label and domain
- Bracketed URLs, no spaces
- One of each header
- List-Post: NO
- List-Id
- RFC 2919
- RFC 2369
By SimpleVerifier Team · Last updated · Runs in your browser; nothing you paste is sent to us
Tidy list headers help readers; a clean list helps delivery.
- When the headers are right, clean the list you are about to send to.
- Upload or paste it at /verify. Every address gets a live mailbox check, and the first 100 email checks are free with a Google sign-in, no card.
How do I check the list headers of a newsletter?
- Send a test issue to a mailbox you own and open its full headers.
- Paste them in. Folded lines are joined for you.
- Read the finding for List-Id and for each List- header the tool found.
- Fix the sending tool's settings if a header is duplicated, a URL is not in angle brackets or the List-Id uses a domain you do not control.
Example
- You enter
- Headers with
List-Id: Example news <news.example.org>, List-Unsubscribe with an https and a mailto URL, List-Help andList-Post: NO. - You get
- Four list headers read, no problems. The List-Id sits under the From domain example.org, and each URL header is a comma-separated set of angle-bracket URLs with nothing inside the brackets but the URL.
- Limits
- Runs in your browser; nothing is uploaded.
What is a List-Id?
RFC 2919 defines the List-Id header: an optional description, then the list identifier in angle brackets, written list-label.namespace. The namespace is a domain name the list owner has authority over, or localhost for lists that are not managed. Identifiers not ending in .localhost must be globally unique, and a message carries no more than one List-Id.
What are the other list headers?
RFC 2369 defines List-Help, List-Unsubscribe, List-Subscribe, List-Post, List-Owner and List-Archive. Each holds one or more URLs in angle brackets, separated by commas, with the most preferred first and no space inside the brackets. List-Post may instead be the word NO. A message carries at most one of each. One-click unsubscribe adds a separate List-Unsubscribe-Post header, covered by the List-Unsubscribe header generator.
Why compare List-Id with the From domain?
RFC 2919 says never to create identifiers in a domain you have no authority over. The tool cannot see who owns a domain, so it shows a note when the List-Id is not under the From domain, for you to confirm. Keeping the identifier under your own domain and leaving it unchanged helps readers who filter mail by list.
Who uses this tool, and for what?
- Cold email senders
- Check the list headers your newsletter or sequencer writes on mail to subscribers.
- Deliverability consultants
- Find duplicated or malformed list headers in a client's sending setup.
- Sales ops
- Confirm a List-Id sits under the company's own domain.
What can’t this tool tell you?
- It checks syntax; it cannot tell who owns the domain in a List-Id or whether a link works.
- It does not check one-click unsubscribe, which has its own header and rules.
- Unusual URL schemes are noted, not rejected.
- The tool follows RFC 2919 and RFC 2369 as written; later updates are not included.
Common questions
- Is List-Id required?
- The standard defines it as an optional header. It is a way for readers and filters to identify a list.
- Can I change my List-Id later?
- RFC 2919 says you may, but that it is not desirable, and that you should avoid changing it even if the sending host changes.
- What does List-Post: NO mean?
- RFC 2369 allows that value to say the list does not accept posts.
- Does List-Id replace List-Unsubscribe?
- No. They are separate headers. List-Id names the list; List-Unsubscribe says how to leave it.
- Why must each header appear once?
- Both RFCs say there must be no more than one of each field in a message, and the tool flags duplicates.
- Is my text sent anywhere?
- No. The headers are read in your browser.
Sources
A tidy list can still be full of dead addresses.
Extracting, deduplicating and syntax checks all work on the text of an address. None of them can tell whether the mailbox exists. Only the server that hosts it can answer that, through an SMTP check, and that is what the paid product does.
- Upload the cleaned file as it is: CSVs up to 100,000 rows
- A real SMTP mailbox check on every row, with catch-all detection
- Small list? Starter at $9/mo covers 2,500 emails a month, cancel anytime
Plans from $9 a month, cancel anytime, no contract. Sign in with Google and your first 100 email checks are free, no card. The free tools stay free either way.