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B2B contact list quality guide: the 6 signals that separate good data from bad, how to audit a list before buying, and Quarvio's verification standards.
Sarah Okonkwo
Email deliverability consultant, 7 years in B2B outbound · Updated June 24, 2026
Last updated: June 2026 · Sarah Okonkwo, Email deliverability consultant, 7 years in B2B outbound
TL;DR — 5 things to know before reading
Seven years of deliverability consulting for B2B outbound teams has given me a clear pattern: the teams that consistently produce strong cold email results are not necessarily the ones with the best copy, the most optimized sequences, or the most aggressive sending volume. They are the ones who are uncompromising about contact data quality.
The reason is structural. Email sending infrastructure — domains, inboxes, and warmup reputation — is fragile in the early stages and slow to rebuild once damaged. A single campaign sent to a low-quality contact list can produce enough hard bounces and spam complaints to destroy months of warmup work in 48 hours. The math is unforgiving: a 5% hard bounce rate on a 2,000-contact send produces 100 bounces, which is enough to trigger reputation flags at Google and Microsoft that affect all subsequent sends from that domain.
The 6 quality signals in this guide are the specific, measurable characteristics that distinguish a contact list that will protect your sending infrastructure from one that will damage it. Each signal has a threshold: above the threshold is safe, below it is risky. Knowing these thresholds before purchasing or using a contact list is the most efficient deliverability investment a cold email team can make.
Bounce rate is the most direct quality indicator, but it is a lagging metric: you only know it after you have already sent to the list. The pre-send proxy for bounce rate is the SMTP verification result, which predicts deliverability without requiring an actual send.
What to look for:
The threshold: Hard bounce rate above 2% on any sending domain should trigger immediate campaign pause and domain investigation. Above 5% is a domain reputation emergency — the domain is likely already being flagged by recipient mail servers.
How Quarvio addresses this: Quarvio performs SMTP verification at order time and provides a 90% deliverability guarantee. For contacts ordered and sent within 60 days, bounce rates reliably fall under 1%. See our email list verification guide for the complete verification methodology.
Catch-all domains accept email to any address at the domain, whether or not the specific mailbox exists. They are common among mid-market companies and professional services firms. SMTP verification cannot confirm whether a specific mailbox at a catch-all domain exists, because the server accepts the verification probe regardless.
What to look for:
The threshold: Catch-all addresses should be segmented separately and sent from a secondary domain. Sending catch-all addresses from your primary sending domain mixes an unknown-quality segment with your verified segment, making bounce rate monitoring unreliable.
How Quarvio addresses this: Quarvio returns catch-all addresses with a separate flag from the verified-clean segment. This allows you to import the two segments into different Instantly campaigns with different sending domain assignments.
B2B data decays as people change jobs, companies shut down, and email addresses are deprovisioned. The freshness date tells you when the contact information was last verified, which determines how much decay has occurred since then.
What to look for:
Decay rate by tenure:
Per Mailmodo's B2B email marketing statistics, B2B email data decays at approximately 22.5% annually. Applying this rate:
| Data age | Estimated remaining validity |
|---|---|
| Under 3 months | 94–97% valid |
| 3–6 months | 89–94% valid |
| 6–12 months | 78–89% valid |
| 12–18 months | 67–78% valid |
| 18–24 months | 56–67% valid |
| Over 24 months | Under 56% valid |
A list that was 95% valid when originally collected becomes progressively less valid over time regardless of the provider's reputation at the time of purchase.
The threshold: For cold email campaigns, use only lists verified within the last 6 months. Lists verified 6–12 months ago should be re-verified before use. Lists over 12 months old should be fully re-verified before any send.
How Quarvio addresses this: Quarvio verifies contacts at order time, meaning the data freshness clock starts when the order is processed, not when the contact was originally collected. This is meaningfully different from providers who collect data once and sell it repeatedly without re-verification.
Verification quality varies significantly between providers. There are three levels of verification (syntax, domain, SMTP), and the label “verified” is applied inconsistently across the industry — some providers call syntax-level checks “verified” despite not performing SMTP-level mailbox confirmation.
What to look for:
The risk of shallow verification: A provider that performs only syntax and domain checks will return a list where 85–95% of addresses “pass” verification but actual SMTP-confirmed deliverability may be 70–80% or lower. The missing 15–20% produces hard bounces.
How Quarvio addresses this: Quarvio performs full SMTP-level verification and provides a 90% deliverability guarantee that is specific to the SMTP verification result, not just domain or syntax checks.
Role-based email addresses are those associated with a job function rather than an individual: info@, sales@, support@, admin@, hello@. These addresses typically route to shared inboxes, ticketing systems, or auto-responders. They are not individual decision-makers.
Role-based addresses in a cold email list are wasted sends at best and reputation-damaging at worst: shared inboxes are more likely to have emails reported as spam because multiple people with different contexts see the same email, some of whom will mark it as unwanted.
What to look for:
The threshold: Role-based addresses should be under 3% of any contact list used for cold email. If the list has a higher percentage, filter them out manually before importing to Instantly.
How to identify role-based addresses: In a spreadsheet, use a filter formula that checks the local part of the email address against a list of common role-based prefixes (info, sales, support, hello, admin, contact, team, marketing, hr, enquiries). Flag these for exclusion.
Contact list quality includes not just technical deliverability but relevance: the percentage of contacts on the list that match the actual target profile. A list with 98% deliverability and 40% ICP match rate will produce low reply rates not because of deliverability issues but because 60% of recipients have no reason to engage.
What to look for:
The threshold: Spot-check 50 random contacts from any list before full import. If more than 10% do not match the intended ICP profile, the filtering was insufficiently precise at the sourcing stage.
How Quarvio addresses this: Quarvio's filtering UI applies job title, seniority, company size, industry, geography, and department filters simultaneously. The combination of multiple simultaneous filters produces a higher ICP match rate than single-dimension filtering, because a contact must match all specified criteria simultaneously to be included.
Whether the list comes from Quarvio, another provider, or an existing internal database, this pre-campaign audit process catches quality problems before they damage sending infrastructure.
Audit step 1: Check the data freshness date
Confirm when the contacts were verified or collected. If the date is over 6 months ago, re-verify before using.
Audit step 2: Scan for role-based addresses
Filter the email column for addresses starting with: info, sales, support, admin, hello, contact, team, enquiries, marketing. Remove these from the campaign list.
Audit step 3: Check catch-all status
If the list comes from a provider that flags catch-all addresses, segment these to a separate file before import. Send catch-all contacts from a secondary domain only.
Audit step 4: Spot-check 50 contacts
Manually verify 50 random contacts: does the company exist, is the company size correct, does the job title match the intended decision-maker layer? If more than 5 contacts fail this check, audit the filtering criteria used to generate the list.
Audit step 5: Validate format
Confirm the CSV uses clean UTF-8 encoding with no BOM, columns are labeled correctly (first_name, last_name, email, company, title), and there are no duplicate email addresses. Duplicates in a list will result in the same person receiving multiple emails in the same sequence if not deduplicated before import.
Audit step 6: Test with 100–200 sends before full scale
Even after a clean audit, monitor bounce rate on the first 100–200 sends from any new list. If bounce rate exceeds 2% on initial sends, pause the campaign and re-verify before continuing.
Some providers offer deliverability guarantees as a marketing statement without defining what the guarantee covers. A meaningful deliverability guarantee should specify:
Quarvio's 90% deliverability guarantee covers items 1–3 above: SMTP-level verification at order time with a 90% valid mailbox threshold. For context on how this compares to industry norms, see our guide to building a B2B prospect list which covers the full list building and validation workflow.
| Need | Tool | Notes |
|---|---|---|
| Pre-verified B2B contacts | Quarvio | SMTP verification at order time, catch-all flagged separately, 90% deliverability guarantee |
| Email inboxes | Inframail | Correct authentication (SPF, DKIM, DMARC) protects domain reputation |
| Cold email sending | Instantly | Per-campaign bounce tracking reveals list quality signals in real time |
| LinkedIn outreach | Aimfox | LinkedIn parallel channel reduces reliance on single-channel list quality |
How do I know if a B2B data provider is performing real SMTP verification or just domain checks?
Ask them directly: “Do you perform SMTP-level mailbox verification, or only domain MX record checks?” A provider that performs genuine SMTP verification can explain the process clearly and can tell you what percentage of their database is flagged as catch-all vs. verified clean. A provider that does not distinguish between catch-all and verified addresses is not performing full SMTP verification. You can also test a small sample: send to 100 contacts from the provider and measure the first-send bounce rate. Under 2% indicates strong SMTP verification; above 5% suggests domain-level verification only.
What should I do if I have already sent to a low-quality list and damaged my domain?
Stop all sends immediately from the affected domain. Check Google Postmaster Tools for spam rate and domain reputation data. Check MXToolbox Blacklist Checker to see if the domain has been added to any email blacklists. If the domain is blacklisted: delist from each blacklist (most have a web form), then extend the sending warmup on a new domain over 4–6 weeks at progressively higher volumes. If the domain is not yet blacklisted but reputation is degraded: stop cold sends, send only to warm contacts for 2–3 weeks, and use that period to re-verify the contact list before resuming cold sends.
Can I improve the quality of a low-quality list I already have?
Yes, through re-verification. Run the list through an SMTP-level verification service to identify and remove invalid addresses. Remove catch-all addresses to a separate file. Remove role-based addresses. After this cleaning process, a list that started at 75% valid may improve to 85–90% valid, which is generally safe for cold email. The remaining question is data freshness: if the list is old, re-verification will remove addresses that have already become invalid, but cannot identify addresses that appear valid today but will bounce because the mailbox is about to be deprovisioned.
How often should I refresh my B2B contact data?
For ongoing outbound programs: refresh the contact list every 12 months at minimum. For industries with high staff turnover (early-stage startups, sales roles, agency roles): refresh every 6–9 months. For lower-turnover industries (healthcare, government, manufacturing): a 12–18 month refresh cycle is acceptable. The practical approach with Quarvio is to order contacts close to the date you plan to send, rather than building a large stockpile of data and using it over 18–24 months, which allows the decay to accumulate.
Start every campaign with verified data — protect the infrastructure you built.
Quarvio delivers SMTP-verified B2B contacts with a 90% deliverability guarantee, catch-all addresses flagged separately, and verification performed at order time. One-time purchase. No subscription. Credits valid 12 months.
