Bounced email extractor: turn bounce messages into a suppression list
Paste the bounce messages (or upload .eml, .mbox or a bounce log) and the tool lists every recipient that bounced, with its SMTP code. Hard bounces such as 5.1.1 go in a suppression list to remove; 4.x.x soft bounces are marked for retry; 5.7.x policy blocks are kept, because they are about your sending, not the address.
By SimpleVerifier Team · Last updated · Runs in your browser; nothing you paste is sent to us
How do I get a list of bounced email addresses?
- Collect the bounces: in Gmail, search
from:mailer-daemonand open each message (or export them with Google Takeout as .mbox); in Outlook, search for "Undeliverable". A CSV bounce log from your sending tool works too. - Paste the text or upload the file. Add your own address or domain so the sender isn't listed.
- Press Find the bounced addresses. Each address is listed once, with its strongest code and the line it came from.
- Download the suppression list (hard bounces and dead mailboxes) and add it to your sending tool's suppression or do-not-contact list.
- Before the next send, check the rest of the list so it doesn't produce the same pile; your first 100 email checks are free with a Google sign-in.
Should I remove hard bounces from my email list?
Yes. A hard bounce is a permanent failure, class 5 in RFC 3463 terms: 5.1.1 (no such user), 5.1.2 (bad domain) or 5.1.10 (null MX) mean the address can't receive mail, and every retry is another bounce against your sender reputation. Mailbox codes in the 5.2.x group (disabled, full for a long time) are usually abandoned inboxes and go on the same list.
The exception is 5.7.x. Those are security and policy refusals: a blocklisted IP, a failed DMARC check, a message rejected as spam. The mailbox may be fine, so deleting it throws away a real contact. Fix the sending problem instead; the bounce message analyzer explains a single message in detail.
Should I remove soft bounces from my email list?
Not after one. A soft bounce (4.x.x) is temporary: a full mailbox, a server that's down, greylisting or a rate limit. Your sending server retries on its own for a period, and most platforms suppress an address only after it soft-bounces repeatedly; Mailchimp, for example, cleans an inactive contact after 7 soft bounces (soft vs. hard bounces).
Keep the retry list and run it again after the next campaign. An address that appears soft-bouncing every time for weeks is effectively dead; move it to the suppression list then. Handling soft bounces covers the timings.
How do I find bounced emails in Gmail or Outlook?
In Gmail, bounces arrive from mailer-daemon@googlemail.com with the subject "Delivery Status Notification (Failure)", so a from:mailer-daemon search lists them. Open one and copy the whole message, or select several in a Takeout .mbox export and upload that. In Outlook, they arrive as "Undeliverable:" messages from the postmaster of the receiving system.
Either way, the useful part is the delivery status block defined in RFC 3464: Final-Recipient, Status and Diagnostic-Code. This tool reads those fields where present, and falls back to the human-readable "wasn't delivered to" lines Gmail and Outlook show above them.
Which bounces go on the suppression list?
| Code | Meaning | What this tool does |
|---|---|---|
5.1.1, 5.1.2, 5.1.10 | No such user, bad domain, null MX | Remove |
5.2.x | Mailbox disabled or full | Remove |
4.x.x | Temporary failure | Retry |
5.7.x | Policy, reputation or authentication block | Keep, fix your sending |
| No code | Read the message | Unclear, unless a phrase like "address not found" settles it |
Who uses this tool, and for what?
- Cold emailers
- Turn a week of mailer-daemon replies in the sending inbox into a suppression list before the next campaign from that domain.
- Small businesses
- Clean up after a mail merge from Gmail or Outlook, where bounces only arrive as messages, not as a report.
- Marketing ops
- Merge bounce logs from two platforms during a migration into one suppression file.
What can’t this tool tell you?
- Runs entirely in your browser; nothing you paste is sent anywhere. Very large pastes are read up to 2 MB of text.
- An address mentioned in a bounce without a code or a clear phrase is listed as unclear, not removed.
- Some servers put a misleading code on a policy block; when the text names a blocklist or spam, the tool keeps the address.
- This lists past bounces; it can't tell which of the rest of your list will bounce next. That needs a mailbox check.
Common questions
- Should I remove hard bounces from my email list?
- Yes. Hard bounces such as 5.1.1 user unknown are permanent, and resending counts against your sender reputation each time. The exception is 5.7.x policy blocks, which are about your sending rather than the address.
- Should I remove soft bounces from my email list?
- Not after a single soft bounce. Retry, and suppress the address only if it keeps soft-bouncing over several sends or weeks.
- How to get bounced emails in Gmail?
- Search from:mailer-daemon in Gmail. Each "Delivery Status Notification (Failure)" message names the address that bounced and the server's reason; paste them into this tool to list them all at once.
- Why am I getting bounced emails?
- Either the address is bad (user unknown, domain gone), the mailbox can't take mail (full, disabled), or the receiving server blocked your message (policy, reputation, authentication). The SMTP code in the bounce tells you which.
Sources
Clean the list before the next send.
A bounce report only tells you about the addresses you already mailed. The rest of the list has the same kinds of dead mailboxes in it, and each one becomes a hard bounce recorded against your domain the moment you send.
- A real SMTP mailbox check on every row, before anything is sent
- Dead and mistyped addresses split out, so they never reach your sending tool
- Catch-all, disposable and role addresses flagged alongside
One plan, 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.