Email List Validation & Domain Health
Stop bad data from burning your sender reputation.
Five-layer email validation, bounce-risk scoring, and continuous domain health monitoring - so every record you send to has been vetted before it touches your outbound infrastructure. One-off validation from £800. Ongoing protection from £1,200/mo.
80+ agencies protected from deliverability damage this year
Risky records quarantined with reason codes - never deleted. You stay in control.
Your bounce rate is climbing. Your reputation is dropping.
You built a pipeline of 50,000 contacts. Your enrichment tool says they are all valid. Then you launch an outbound campaign and 3.8% bounce. Your domain gets flagged. Your next campaign lands in spam - even the messages going to real, engaged prospects. One bad send poisons the well for months.
Standard verification tools check whether a mailbox exists at the moment you ask. They do not tell you that the domain is on a blocklist, that it is a catch-all accepting everything, or that the address will bounce next week when the temporary inbox gets shut down. You get a green tick today and a blacklist tomorrow.
The cost is not just bounced emails. It is lost deals, wasted ad spend, and weeks rebuilding sender reputation that took months to earn. Every campaign you send through an unvalidated list is a gamble with your domain - and most agencies do not realise how bad the odds are until the damage is done.
How we protect your deliverability
A systematic approach to eliminating bounce risk - from initial audit through ongoing monitoring.
01List intake & baseline audit
List intake & baseline audit
List intake & baseline audit
You send us your list - exported from your CRM, marketing platform, or enrichment tool. We run a baseline audit to measure current bounce risk, flag obvious problems (syntax errors, known spam traps, disposable domains), and establish your starting health score. This gives both of us a clear picture of how much risk is sitting in your pipeline before we start the deep validation.
02Five-layer validation
Five-layer validation
Five-layer validation
Every record passes through five validation layers: syntax check for formatting and typos, domain verification via MX and DNS records, SMTP-level mailbox testing without sending, catch-all domain analysis, and a composite bounce-risk score from 0 to 100. We throttle verification carefully to avoid triggering spam traps or rate limits on receiving domains. The result is a clear verdict on every single address.
03Quarantine & risk report
Quarantine & risk report
Quarantine & risk report
Risky records are quarantined - never deleted. Each flagged address comes with a reason code: hard bounce risk, disposable domain, role-based address, catch-all uncertainty, or blocklist association. You get a full report with actionable recommendations, not just a pass/fail spreadsheet. You decide what stays, what goes, and what gets re-verified later.
04Domain health monitoring
Domain health monitoring
Domain health monitoring
On retainer plans, we set up continuous monitoring of your sending domains and client domains. Monthly reporting covers sender reputation metrics, blocklist status across major providers, and trend analysis on bounce rates. If your domain reputation drops or a blocklist flags you, we send a proactive alert with root-cause analysis - not just a notification, but a diagnosis and fix. One-off projects receive a point-in-time snapshot instead.
What you receive
Concrete outputs - not vague assurances. Every engagement produces documented, auditable results.
Validated contact list
Every record scored 0-100 for bounce risk, with a clear safe/risky/remove verdict and reason codes for every flag.
Quarantine file with reason codes
All risky records isolated in a separate file with specific explanations - hard bounce, disposable domain, role-based, catch-all, or blocklist match.
Domain health report
MX record status, DNS configuration, blocklist presence, and sender reputation score for every sending domain in your list.
Bounce-risk analysis
Root-cause breakdown of why your list carries risk - data source quality, age decay, domain patterns - with recommendations to reduce future bounce rates.
Monthly monitoring dashboard
Retainer clients receive ongoing tracking of sender reputation, blocklist status, bounce rate trends, and proactive alerts when anything changes.
How many invalid records are hiding in your pipeline?
One-off validation from £800. No ongoing commitment required.
Find out in 48 hoursBuilt for teams dealing with this
If any of these sound familiar, your deliverability is already at risk.
"Our bounce rate just spiked to 4% and we don't know why."
You launched a campaign that looked clean. Now your domain is flagged and even good contacts are landing in spam. We validate before you send so spikes never happen.
"We're getting blacklisted after every big send."
Blocklists do not warn you - they just flag your domain and your deliverability collapses overnight. We monitor blocklist status continuously and catch problems before your next campaign goes out.
"Our enrichment tool says everything is valid, but emails still bounce."
Enrichment tools check mailbox existence at the moment of lookup. They do not catch catch-all domains, temporary inboxes, or addresses that will go stale next week. Our five-layer validation goes deeper.
"We manage outbound for multiple clients and can't risk cross-contamination."
One client's bad list can damage the sending reputation you use for all your accounts. We validate and monitor each client domain separately so one bad list never poisons the rest.
"We bought a list and need to know what's actually usable."
Purchased lists are the highest-risk data source in B2B. We score every record 0-100, quarantine the risky ones with reason codes, and give you a clean, sendable subset - typically 70-85% of the original list.
"Our open rates have been declining for months and we can't figure out why."
Declining open rates are often a deliverability problem, not a content problem. If your domain reputation has been quietly eroding, your emails are going to spam. We diagnose the root cause and fix the data layer.
What Clients Say
“We were sitting at a 3.6% bounce rate and had no idea why. ContactWise validated our list, quarantined 1,400 risky records, and our next campaign bounced at 0.3%. Should have done this six months earlier.”
Kate Hargreaves,
Head of Marketing, B2B lead gen agency (45 employees)
“We manage outbound for 12 clients. One client's purchased list got us blacklisted on Spamhaus and it affected all our other accounts. ContactWise now validates every list before it enters our system. Zero blacklist incidents since.”
Rob Merton,
Operations Director, Sales outsourcing firm (60 employees)
“Our enrichment provider said our data was 98% valid. ContactWise found 2,200 catch-all domains and 340 disposable addresses they had missed. The bounce-risk scoring alone was worth the investment.”
James Linfield,
RevOps Manager, SaaS company (120 employees)
“The domain health report flagged that two of our sending domains had degraded MX configurations. Our IT team had no idea. Fixing those alone improved our inbox placement by 14%.”
Sarah Patel,
Digital Marketing Lead, Recruitment agency (30 employees)
“We send 80,000 emails a month across client accounts. The monthly monitoring catches problems before they become crises. Last month they flagged a blocklist issue at 2am and had it resolved before our morning send.”
David Chen,
CEO, Email marketing agency (25 employees)
“We had been using a basic verification tool for two years and thought we were covered. ContactWise found that 9% of our 'verified' list carried high bounce risk. That is thousands of pounds in wasted send costs we did not know about.”
Laura Brennan,
Head of Demand Gen, Martech company (80 employees)
“The quarantine approach is what sold us. Nothing gets deleted - we see exactly why each record was flagged and decide what to do. Two records they flagged as risky turned out to be our biggest prospect's new domain. We would have lost those.”
Michael Thorpe,
Sales Director, IT services provider (55 employees)
“Turnaround was impressive. We sent 8,000 records on Monday morning, had validated results by Tuesday afternoon. Clean file, quarantine file, domain health report - all clearly documented. No ambiguity.”
Priya Kaur,
Marketing Manager, Financial services consultancy (35 employees)
“We switched from doing our own verification in-house to using ContactWise. Our bounce rate dropped from 2.8% to 0.4% and we freed up about 15 hours a month of ops time. The retainer pays for itself three times over.”
Nick Ashworth,
COO, ABM agency (40 employees)
“They caught a pattern we never would have spotted - a batch of addresses from a single provider were all going stale within 60 days. Turned out to be trial accounts from a freemium tool. That kind of root-cause analysis is not something you get from a standard verification API.”
Emma Griffiths,
Data Operations Lead, Growth agency (50 employees)
“We were sitting at a 3.6% bounce rate and had no idea why. ContactWise validated our list, quarantined 1,400 risky records, and our next campaign bounced at 0.3%. Should have done this six months earlier.”
Kate Hargreaves,
Head of Marketing, B2B lead gen agency (45 employees)
“We manage outbound for 12 clients. One client's purchased list got us blacklisted on Spamhaus and it affected all our other accounts. ContactWise now validates every list before it enters our system. Zero blacklist incidents since.”
Rob Merton,
Operations Director, Sales outsourcing firm (60 employees)
“Our enrichment provider said our data was 98% valid. ContactWise found 2,200 catch-all domains and 340 disposable addresses they had missed. The bounce-risk scoring alone was worth the investment.”
James Linfield,
RevOps Manager, SaaS company (120 employees)
“The domain health report flagged that two of our sending domains had degraded MX configurations. Our IT team had no idea. Fixing those alone improved our inbox placement by 14%.”
Sarah Patel,
Digital Marketing Lead, Recruitment agency (30 employees)
“We send 80,000 emails a month across client accounts. The monthly monitoring catches problems before they become crises. Last month they flagged a blocklist issue at 2am and had it resolved before our morning send.”
David Chen,
CEO, Email marketing agency (25 employees)
“We had been using a basic verification tool for two years and thought we were covered. ContactWise found that 9% of our 'verified' list carried high bounce risk. That is thousands of pounds in wasted send costs we did not know about.”
Laura Brennan,
Head of Demand Gen, Martech company (80 employees)
“The quarantine approach is what sold us. Nothing gets deleted - we see exactly why each record was flagged and decide what to do. Two records they flagged as risky turned out to be our biggest prospect's new domain. We would have lost those.”
Michael Thorpe,
Sales Director, IT services provider (55 employees)
“Turnaround was impressive. We sent 8,000 records on Monday morning, had validated results by Tuesday afternoon. Clean file, quarantine file, domain health report - all clearly documented. No ambiguity.”
Priya Kaur,
Marketing Manager, Financial services consultancy (35 employees)
“We switched from doing our own verification in-house to using ContactWise. Our bounce rate dropped from 2.8% to 0.4% and we freed up about 15 hours a month of ops time. The retainer pays for itself three times over.”
Nick Ashworth,
COO, ABM agency (40 employees)
“They caught a pattern we never would have spotted - a batch of addresses from a single provider were all going stale within 60 days. Turned out to be trial accounts from a freemium tool. That kind of root-cause analysis is not something you get from a standard verification API.”
Emma Griffiths,
Data Operations Lead, Growth agency (50 employees)
“We were sitting at a 3.6% bounce rate and had no idea why. ContactWise validated our list, quarantined 1,400 risky records, and our next campaign bounced at 0.3%. Should have done this six months earlier.”
Kate Hargreaves,
Head of Marketing, B2B lead gen agency (45 employees)
“We manage outbound for 12 clients. One client's purchased list got us blacklisted on Spamhaus and it affected all our other accounts. ContactWise now validates every list before it enters our system. Zero blacklist incidents since.”
Rob Merton,
Operations Director, Sales outsourcing firm (60 employees)
“Our enrichment provider said our data was 98% valid. ContactWise found 2,200 catch-all domains and 340 disposable addresses they had missed. The bounce-risk scoring alone was worth the investment.”
James Linfield,
RevOps Manager, SaaS company (120 employees)
“The domain health report flagged that two of our sending domains had degraded MX configurations. Our IT team had no idea. Fixing those alone improved our inbox placement by 14%.”
Sarah Patel,
Digital Marketing Lead, Recruitment agency (30 employees)
“We send 80,000 emails a month across client accounts. The monthly monitoring catches problems before they become crises. Last month they flagged a blocklist issue at 2am and had it resolved before our morning send.”
David Chen,
CEO, Email marketing agency (25 employees)
“We had been using a basic verification tool for two years and thought we were covered. ContactWise found that 9% of our 'verified' list carried high bounce risk. That is thousands of pounds in wasted send costs we did not know about.”
Laura Brennan,
Head of Demand Gen, Martech company (80 employees)
“The quarantine approach is what sold us. Nothing gets deleted - we see exactly why each record was flagged and decide what to do. Two records they flagged as risky turned out to be our biggest prospect's new domain. We would have lost those.”
Michael Thorpe,
Sales Director, IT services provider (55 employees)
“Turnaround was impressive. We sent 8,000 records on Monday morning, had validated results by Tuesday afternoon. Clean file, quarantine file, domain health report - all clearly documented. No ambiguity.”
Priya Kaur,
Marketing Manager, Financial services consultancy (35 employees)
“We switched from doing our own verification in-house to using ContactWise. Our bounce rate dropped from 2.8% to 0.4% and we freed up about 15 hours a month of ops time. The retainer pays for itself three times over.”
Nick Ashworth,
COO, ABM agency (40 employees)
“They caught a pattern we never would have spotted - a batch of addresses from a single provider were all going stale within 60 days. Turned out to be trial accounts from a freemium tool. That kind of root-cause analysis is not something you get from a standard verification API.”
Emma Griffiths,
Data Operations Lead, Growth agency (50 employees)
Why agencies choose Deliverability Shield
Proactive, not reactive
Most verification tools tell you an address is bad after you have already bounced. We score risk before you send and monitor continuously so problems are caught early - not after your domain reputation takes the hit.
Full transparency on every flag
Every quarantined record comes with a reason code and a bounce-risk score from 0 to 100. You see exactly why an address was flagged and decide what to do with it. Nothing is hidden, nothing is deleted without your sign-off.
Five layers deep, not one
Syntax check, domain verification, SMTP test, catch-all analysis, and composite bounce-risk scoring. Standard tools stop at one or two layers. We run all five on every record because a single check is never enough.
UK-based team, UK data expertise
Based in the UK, familiar with UK domain infrastructure, ISP behaviour, and data regulations. Your data is handled by a team that understands your market - not routed through offshore verification APIs.
Simple pricing. No per-record games.
Choose the level of protection that matches your sending volume and risk tolerance.
One-Off Validation
£800
Up to 10,000 records. One-time validation with full reporting.
- Five-layer validation on every record
- Bounce-risk score (0-100) per address
- Quarantine file with reason codes
- Domain health report
- 24-48 hour turnaround
- Actionable recommendations
Monthly Shield
£1,200/mo
Up to 25,000 records. Ongoing monitoring and monthly re-validation.
- Everything in One-Off Validation
- Monthly list re-validation
- Continuous domain health monitoring
- Blocklist tracking & proactive alerts
- Sender reputation trend reporting
- Root-cause analysis on bounce patterns
- Priority email support
Agency Shield
£2,200/mo
Up to 100,000 records. Multiple client domains with per-client reporting.
- Everything in Monthly Shield
- Multiple client domain monitoring
- Cross-domain contamination prevention
- Per-client reporting and quarantine
- Up to 100,000 records per month
- Priority support with dedicated contact
- Custom alert thresholds per domain
Not sure which tier fits? We will assess your current bounce risk and recommend the right level of protection.
Larger lists or custom requirements? Book a free scoping call — we’ll tailor the engagement.
Frequently asked questions about Deliverability Shield
Every record goes through five layers of validation: syntax check (formatting and typos), domain verification (MX records and DNS health), SMTP test (mailbox existence without sending), catch-all analysis (flagging domains that accept everything), and bounce-risk scoring (a 0-100 score based on all signals combined). You get a clear verdict on every address.
24-48 hours depending on list size. Smaller lists (under 10,000 records) typically come back within a day. Larger lists take closer to 48 hours because we throttle verification to avoid triggering spam traps or rate limits on the receiving domains.
Risky records are quarantined with reason codes - never deleted. You'll see exactly why each address was flagged (hard bounce risk, disposable domain, role-based address, etc.) and you decide what to do with them. We don't touch your live lists without your sign-off.
Yes, on retainer plans. We run ongoing domain health checks, monthly reporting on sender reputation metrics, and proactive alerts if your domain reputation drops or blacklist status changes. One-off projects get a point-in-time snapshot instead.
Yes. We validate the output from any source - your CRM, marketing automation platform, purchased lists, enrichment tools - before it sends. Think of it as a final quality gate that sits between your data and your outbound infrastructure.
Most verification tools give you a pass/fail on individual addresses. We go deeper: domain health monitoring, sender reputation tracking across major blocklists, root-cause analysis on why bounces are happening, and ongoing protection - not just a one-time check. It's the difference between verifying an address and protecting your deliverability.
CSV or Excel. We need at minimum an email column, but the more context you provide (name, company, source, date added) the better our analysis. We can pull exports directly from most CRMs and marketing automation platforms if you prefer.
Catch-all domains accept any address, which means standard SMTP verification always returns a false positive. We flag these separately with a catch-all risk score based on domain age, traffic patterns, and historical bounce data. You get a clear recommendation on whether to send, suppress, or re-verify later.
No. We use non-intrusive SMTP handshake verification - we check whether the mailbox exists without actually sending an email. Our verification is throttled to avoid rate limiting and we rotate our checking infrastructure to prevent any flags on your domain or ours.
Absolutely - and you should. Purchased lists are the highest-risk data source in B2B outbound. We typically find 10-30% of purchased list records carry some level of bounce risk. Running them through validation before your first send protects your domain from day one.
Your next campaign is only as good as the data behind it.
Find out how many risky records are hiding in your pipeline. One validation run is all it takes to see the difference between what your tools say is clean and what actually is.
30-minute scoping call. We assess your bounce risk and recommend the right level of protection.Every unvalidated send is a gamble with your domain reputation.
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