From and Reply-To header checker for your test email
In short: Paste the headers of a test email. The tool reads each mailbox in From, Sender, Reply-To and Return-Path, checks the counts and the rules in RFC 5322, and compares the domains. Limit: It checks header syntax and counts, not whether the mailbox exists or the domain authenticates.
Paste the headers of a test email. The tool lists the mailboxes in From, Sender, Reply-To and Return-Path and checks them against RFC 5322: one From, Sender present when From has several mailboxes, at most one Reply-To. It also flags a display name that contains a different address and a Reply-To or Return-Path on another domain.
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
Three mailboxes read with no problems; replies go to a different domain from the From address.
- Problems
- 0
- Mailboxes read
- 3
- From domain
- example.org
What this means for you
That is allowed, so it is shown as a note to confirm the inbox is monitored.
- One From, at most one Reply-To
- Sender when From has several
- Display name holding an address
- Return-Path domain
- From
- Reply-To
- RFC 5322
By SimpleVerifier Team · Last updated · Runs in your browser; nothing you paste is sent to us
The right From address still needs a clean list.
- 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 these headers?
- Send a test email to a mailbox you own and open its full headers.
- Paste them in. Folded lines are joined for you.
- Read the mailboxes the tool found and the findings under them.
- Change the From name, the Reply-To address or the bounce address in your sending tool if a finding shows something you did not intend.
Example
- You enter
- Headers with
From: "Example Sales" <sales@example.org>,Reply-To: replies@example.netandReturn-Path: <bounce@mail.example.org>. - You get
- Three mailboxes read, no problems. One note: replies go to example.net, a different domain from the From domain example.org. The Return-Path domain mail.example.org can align with the From domain.
- Limits
- Runs in your browser; nothing is uploaded.
What does RFC 5322 say about From, Sender and Reply-To?
RFC 5322 says a message has exactly one From header, listing one or more mailboxes. When From lists more than one mailbox, a Sender header with a single mailbox must be present. Reply-To is optional and a message carries at most one. The tool checks those counts and that each address is well formed.
Why check the display name?
Readers see the display name before the address. A name such as "billing@example.com" in front of a different real address can look like impersonation, so the tool flags a display name that holds an address which is not the one the message is sent from. This is a practical warning, not a rule in the standard.
What about Reply-To and Return-Path on another domain?
Both are allowed. Replies often go to a different mailbox, and the Return-Path is the bounce address that SPF is checked against, so for SPF to count towards DMARC the Return-Path domain has to align with the From domain. The tool shows a note when the domains differ. The DMARC alignment checker goes further.
Who uses this tool, and for what?
- Cold email senders
- Confirm the From name and Reply-To your sequencer actually writes.
- Deliverability consultants
- Spot a display name that carries a second address in a client's template.
- Sales ops
- Check that replies from a campaign will land in the shared inbox.
What can’t this tool tell you?
- It checks header syntax and counts, not whether the mailbox exists or the domain authenticates.
- Group syntax and obsolete address forms are not fully read.
- Domain matching treats a domain and its subdomains as one family and does not use the public suffix list.
- The tool follows RFC 5322 as written; later updates are not included.
Common questions
- Can a message have two From headers?
- No. RFC 5322 allows exactly one From header, though it can list several mailboxes.
- When is a Sender header required?
- When From lists more than one mailbox, RFC 5322 says a Sender header with one mailbox must appear.
- Is a different Reply-To domain a problem?
- No, it is allowed. The tool shows a note so you can confirm replies reach a mailbox you read.
- Why is there no Return-Path in my draft?
- The receiving server adds it to the stored copy, so it shows in a received message and not in a draft.
- Does the tool check SPF or DKIM?
- No. It reads the header text you paste and makes no DNS lookups.
- 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.