Gmail 'Very Low Reputation of the Sending Domain' (421 4.7.0 / 550 5.7.1): How to Recover
421 4.7.0 This message is suspicious due to the very low reputation of the sending domain means Gmail has judged your domain's recent mail so poorly that it now treats new mail from it as suspicious. With 421 4.7.0 the message is deferred and your server retries. With 550 5.7.1 it is rejected outright. There is no form that resets it. Reputation recovers only as Gmail sees better mail from the domain: lower volume, sent steadily, to people who want it, from a fully authenticated domain, with no invalid addresses. Fix the cause first, then rebuild slowly.
The exact messages
Google's Gmail SMTP errors and codes page (last updated 26 October 2026, read 2 November 2026) lists four versions:
| Code | Message text | What happens |
|---|---|---|
| 421 4.7.0 | "This message is suspicious due to the very low reputation of the sending IP address." | Rate limited, retried |
| 421 4.7.0 | "This message is suspicious due to the very low reputation of the sending domain." | Deferred, retried |
| 550 5.7.1 | "This message is likely suspicious due to the very low reputation of the sending IP address." | Rejected |
| 550 5.7.1 | "This message is likely suspicious due to the very low reputation of the sending domain." | Rejected |
The same code number covers other problems. 421 4.7.0 also means a missing PTR record, a TLS requirement or "try again later". 550 5.7.1 also covers "likely unsolicited email" and malformed headers. Read the text, not just the number, or paste the full bounce into Bounce Doctor.
IP or domain: which one is yours?
| Version | What Gmail rated | Who controls it |
|---|---|---|
| Sending IP | The server that handed over the message | Your ESP, cold email platform or mailbox provider, unless you run your own server |
| Sending domain | The domain in your authentication, usually the DKIM and From domain | You |
If you send from Google Workspace or Microsoft 365 inboxes, the IP belongs to Google or Microsoft, and the domain version is the one that matters. If the IP version names an IP from your platform's shared pool, send the full bounce to the platform. The reverse DNS lookup shows whose IP it is.
Why it happens to cold senders
Google's sender guidelines say "A negative reputation can impact your delivery rate", and that a high spam rate "leads to increased spam classification". They do not publish the formula. These are the usual causes:
| Cause | Why it hurts the domain |
|---|---|
| Spam reports | The strongest negative signal Gmail has |
| Invalid addresses | Many unknown-user bounces say the list was not built with permission |
| Old lists and spam traps | Addresses that have been dead for years can be recycled as traps |
| Volume spikes | A new or quiet domain suddenly sending hundreds a day |
| Every inbox on one domain | Gmail adds them up |
| Low engagement | Mail that is never opened, replied to or moved out of spam |
| Weak authentication | Harder for Gmail to attribute good mail to you |
A domain that went from no history to "very low" in a couple of weeks has almost always been sent too much, too fast, to a list with problems.
Recovery plan
1. Stop the damage
Pause the campaigns sending as that domain to Gmail and Google Workspace addresses. Every rejected or deferred message is more evidence against the domain. Keep sending normal one-to-one mail if you have it: replies and real conversations help.
2. Confirm authentication
The domain should pass SPF and DKIM, have a DMARC record, and the From domain should align with one of them. Gmail requires all three for bulk senders. Run the bulk sender checker for Google's requirements in one pass, and the DMARC alignment checker if you are unsure about alignment.
3. Find the cause in your data
- Bounce rate per campaign. Which list pushed the domain down?
- Replies. Lots of "remove me" or angry replies mean spam reports are likely too.
- Volume history. Did you add inboxes or a new campaign just before it started?
- Postmaster Tools. If the domain has enough volume, Google Postmaster Tools shows the spam rate and the compliance dashboard.
4. Fix the list before you send again
Verify every lead you plan to mail, and suppress every hard bounce, every unsubscribe and everyone who asked not to be contacted. Remove leads older than a few months unless you re-verify them. Our suppression list guide covers what to keep out.
5. Rebuild slowly
Start with a small daily volume to your best-fit, most recent leads, spread through the day. Keep sequences short. Increase in small steps only while bounces stay low and there are no new deferrals. Our sender reputation recovery guide has a week-by-week plan, and improve sender reputation covers the habits that keep it up.
6. Ask for mitigation only when you qualify
Google's sender guidelines FAQ says bulk senders that meet all of its requirements can submit an escalation through the sender contact form, but that they "remain ineligible for mitigation while user-reported spam rate is greater than 0.3%", until it stays below 0.3% for 7 consecutive days.
Should you start over with a new domain?
Sometimes. If the domain is a secondary sending domain, months of bad history are attached to it, and nothing else depends on it, retiring it can be sensible. But a new domain only helps if you change what caused the problem. Gmail's own guidelines warn against sudden volume from senders with no history, so a new domain sent at the old volume to the old list will usually get the same error, faster. Never move the problem to your main company domain.
Mistakes that slow recovery
- Rotating domains every week. Each one gets burned and none recovers.
- Warm-up tools as a fix. Automated warm-up traffic does not replace mail people want.
- Sending more to "push through". Deferred mail is retried; more mail means more deferrals.
- Changing the From name or subject lines only. Reputation sits on the domain, not the copy.
How to tell it is improving
Reputation does not come back with a notice. Watch these instead:
| Signal | What improvement looks like |
|---|---|
| Bounces from Gmail | Fewer 421 4.7.0 deferrals, then none, at the same daily volume |
| Rejections | No new 550 5.7.1 reputation rejections |
| Replies | Reply rate from Gmail and Workspace recipients returns towards your other domains |
| Seed inbox | A test message to a Gmail account you own lands in the inbox, not spam |
| Postmaster Tools | Spam rate stays well under 0.10%, if the domain has enough volume to show data |
If none of these move after two or three weeks of low, clean sending, look again at the list source and the targeting. Something in the mail itself is still generating complaints.
Where SimpleVerifier fits
Verification will not raise a reputation on its own. It removes bad addresses, which are one of the things that lowered it. SimpleVerifier runs a live mailbox check on each address and returns safe to send, send with care, check again later or do not send, with the reason. Catch-alls stay risky, never guessed valid, so your rebuild sends go to addresses a server confirmed.
The first 100 checks are free with a Google sign-in on the verify page. Pro is $39 a month with the first 100,000 checks a month at full speed, then slower, never cut off. See pricing.
Common questions
What does 'very low reputation of the sending domain' mean?
Gmail has rated the domain in your message's authentication so poorly that it treats mail from it as suspicious. With 421 4.7.0 the message is deferred and your server will retry; with 550 5.7.1 it is rejected. The usual causes are spam reports, sending to invalid or old addresses, and sudden volume.
How long does it take to fix Gmail domain reputation?
Google does not publish a time. Reputation is built from recent mail, so it improves as Gmail sees lower volume, fewer complaints and fewer bounces from the domain. Expect weeks, not days, of careful sending.
Is there a Gmail blacklist removal form?
No. Gmail does not run a public delist process for reputation. Google says bulk senders that meet all of its sender guidelines can submit an escalation through its sender contact form, but not while their user-reported spam rate is above 0.3%.
Should I switch to a new domain?
Only if the domain is beyond use, and only after fixing what caused the problem. A new domain has no reputation, and sending the same list with the same targeting usually gets it to the same place.
What is the difference between the IP and the domain version?
The IP version is about the server that handed over the message. If you send through Google Workspace or a large provider, that IP is theirs. The domain version is about your domain, wherever it sends from, and is the one you control.
Check your list before you send
Real mailbox checks over SMTP, and nothing is sent to the address. Sign in with Google and your first 100 email checks are free, no card. Plans for bigger lists are on the pricing page.