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Email Bounce and Blocklist Explainer
Reads an SMTP bounce and identifies the blocklist that rejected the message, what it means and how removal actually works.
Developer
Nothing uploaded
No sign-up
Free, unlimited
Paste the whole bounce, including any URL it contains.
Paste something on the left to see the result.
In short
An SMTP rejection beginning with 5 is permanent and the message will not be retried; one beginning with 4 is temporary and the sending server will keep trying, usually for a few days. Most rejections that name a blocklist include a URL for checking and delisting, and Spamhaus is by far the most consequential because it is used almost everywhere. The important part is that delisting is the last step rather than the first: every list re-adds an address whose behaviour has not changed, and some treat a premature request as a signal in itself. Paste a bounce into the Bounce Message Explainer on inputtesthub.com and it identifies the list, explains what that particular one means, and links to the right removal page.
How to use the Email Bounce and Blocklist Explainer
- Copy the whole bounce message you received.
- Paste it in.
- Read what the named list means, then fix the cause before requesting removal.
About the Email Bounce and Blocklist Explainer
The Email Bounce and Blocklist Explainer reads an SMTP bounce and identifies the blocklist that rejected the message, what it means and how removal actually works. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.
What people use it for
- Working out which blocklist is blocking your mail.
- Understanding a 5.7.1 rejection.
- Deciding whether a listing is worth appealing.
Details
| 5xx | Permanent — the message is not retried |
|---|---|
| 4xx | Temporary — the sender keeps trying, usually for days |
| Spamhaus | The most widely used list; a listing affects delivery almost everywhere |
| SpamCop | Expires automatically within 24 hours of the last report |
| UCEPROTECT levels 2 and 3 | List whole ranges, and are widely ignored |
| Google and Microsoft | Filter on their own data — no public list to check |
A listing is a symptom. The lists themselves are mostly automated and mostly fair, and an address gets listed because mail from it looked like spam to a trap, a filter or a recipient. Treating removal as the task rather than the cause produces a domain that is delisted on Monday and listed again by Friday.
Where this tool stops
Reads the text you paste and recognises the blocklists that name themselves in a rejection. It performs no DNS lookup, so it cannot tell you whether an address is listed right now — the links it gives do that.
Frequently asked questions
What does 550 5.7.1 mean?
A permanent rejection for policy reasons — the receiving server understood the message and refused it. The text after the code usually says why, and when a blocklist is involved the name and a URL are almost always included. A 5xx code means the message will not be retried, so the sender must fix the cause and send again.
Should I request delisting straight away?
No. Every list will re-add an address whose behaviour has not changed, and some treat a premature request as a negative signal. Find the cause first — a compromised mailbox, a purchased list, a missing unsubscribe link, an open relay, a forwarding loop — fix it, then ask.
I am listed on UCEPROTECT level 3. How bad is that?
Usually not very. Levels 2 and 3 list entire netblocks and autonomous systems, so you can be listed for something an unrelated customer of your host did. Many receivers ignore those levels for that reason, and the paid express delisting they offer is generally not worth buying — the listing expires on its own.
Gmail is rejecting me and no list is named. What now?
Google filters on its own reputation data and publishes no list. Since 2024 bulk senders need SPF, DKIM and DMARC all passing, a working one-click unsubscribe header, and a spam complaint rate below 0.3%. A rejection almost always traces back to one of those four rather than to a blocklist.
Do I need an account to use the Email Bounce and Blocklist Explainer?
There is no cost and no cap. The Email Bounce and Blocklist Explainer is not a demo of a paid product, so nothing is held back or watermarked.
Is what I paste into the Email Bounce and Blocklist Explainer stored?
No. The Email Bounce and Blocklist Explainer runs entirely in your browser using JavaScript. Your input never reaches inputtesthub.com or any third party — open your browser's Network tab while you use it and you will see no request go out.
What problem does the Email Bounce and Blocklist Explainer solve?
Typical uses: working out which blocklist is blocking your mail. Understanding a 5.7.1 rejection. Deciding whether a listing is worth appealing. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
What are the limits of the Email Bounce and Blocklist Explainer?
Reads the text you paste and recognises the blocklists that name themselves in a rejection. It performs no DNS lookup, so it cannot tell you whether an address is listed right now — the links it gives do that. Knowing where a tool stops being trustworthy matters more than the cases where it works.
What are the reference figures here?
5xx is Permanent — the message is not retried. 4xx is Temporary — the sender keeps trying, usually for days. Spamhaus is The most widely used list; a listing affects delivery almost everywhere. These are printed on the page itself, so you do not have to take them on trust.
Can I use the Email Bounce and Blocklist Explainer on mobile?
Yes. The page is responsive and the tool works in Chrome, Safari, Firefox, Edge and Samsung Internet on both Android and iOS. There is no app to install and nothing to sign into.
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