DFY GTM Systems

How to Verify B2B Emails

By Abdul Sami, GTM Engineer · 6 min read · Last updated

B2B email verification has three layers: syntax (is it shaped like an email), domain/MX (can the domain receive mail), and mailbox-level (does this exact inbox exist). Free tools cover the first two; mailbox-level checks use SMTP handshakes from paid verifiers. Verified lists should hold hard bounces under 2%.

Layer 1 Syntax

Pattern-checking catches typos and malformed rows. Instant and free, but only proves the string is shaped like an email.

Layer 2 Domain & MX

Querying MX records confirms the domain accepts mail at all. This removes dead domains, typosquats, and lapsed companies the biggest single source of hard bounces.

Layer 3 Mailbox-level

Paid verifiers open an SMTP conversation and ask the server whether the mailbox exists, without sending. Accuracy runs 95–99% except on catch-all domains, which accept everything and can only be graded 'risky'.

Handling catch-alls

  • Send catch-alls in small batches with tight monitoring.
  • Prioritize them by other signals (recent trigger, seniority).
  • Drop them entirely if your bounce budget is already tight.

FAQ

What is a catch-all email domain?
A server configured to accept mail for any address at the domain. Verification can't confirm individual inboxes there, so results come back 'risky' rather than valid or invalid.
How accurate is email verification?
95–99% on non-catch-all domains from reputable verifiers. Domain/MX checks alone catch the worst 3–8% of a typical raw list.
Does verification hurt my sender reputation?
No verification doesn't send email. It protects reputation by preventing the bounces that damage it.
AS

Abdul Sami

GTM Engineer, DFY GTM Systems

7+ years building outbound systems for B2B companies across the US, UK, Australia, and DACH. Specializes in Clay workflows, cold email infrastructure, intent-based lead sourcing, and deliverability.

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