Verifying Custom Domain Email Addresses
Most B2B email addresses use custom domains — contact@company.com rather than @gmail.com. Verifying custom domain addresses is the core use case for email verification services, and it's where VeriMails' catch-all probability scoring provides the most value.
Verification Challenges
Custom domain email presents the full spectrum of verification challenges. The underlying provider can be anything — Google Workspace, Microsoft 365, self-hosted, or smaller providers like Zoho, Fastmail, or Rackspace. Each behaves differently. The biggest challenge is catch-all: a significant percentage of business domains are configured as catch-all, meaning every address appears deliverable at the SMTP level. Without catch-all scoring, 20-40% of your B2B email addresses remain unverifiable by traditional methods.
How VeriMails Handles Custom Business Domains
VeriMails first identifies the underlying email provider through MX record analysis. We detect Google Workspace, Microsoft 365, Zoho, Fastmail, Rackspace, cPanel, Plesk, and dozens of other providers. Each receives provider-specific verification logic that accounts for their unique SMTP behaviors. For catch-all domains, we apply our pattern scoring algorithm. This analyzes naming conventions, cross-references with known patterns, and assigns a probability score (0-100) for each address. For non-catch-all domains, standard SMTP verification provides definitive valid/invalid results.
Tips for Custom Business Domains Verification
Custom domain verification accuracy depends heavily on the underlying provider and catch-all configuration. Non-catch-all domains verify with 95%+ accuracy regardless of provider. Catch-all domains benefit most from VeriMails' probability scoring — this is where we provide the most value compared to other verifiers. If you're verifying B2B lists, expect 20-40% of domains to be catch-all. VeriMails turns these from unknowns into actionable probability scores.
What Results to Expect
Custom domains (non-catch-all): 95%+ definitive valid/invalid. Custom domains (catch-all): probability scores (0-100) per address. Provider detection accuracy: 99%+. Overall, custom domain verification is VeriMails' strongest use case because catch-all scoring delivers the most incremental value here.
Frequently Asked Questions
How does VeriMails know which provider a domain uses?
We analyze MX records to identify the underlying email infrastructure. Google Workspace, Microsoft 365, and other major providers have distinctive MX records. This lets us apply provider-specific verification logic for maximum accuracy.
Why are so many business domains catch-all?
IT administrators enable catch-all to avoid missing legitimate emails sent to misspelled or outdated addresses. Common configurations in Microsoft 365 and Google Workspace default to or easily enable catch-all. This is especially common in mid-size companies.
What makes catch-all scoring valuable for B2B?
Without scoring, verifiers mark 20-40% of B2B addresses as 'unknown.' VeriMails' probability scoring turns these into actionable data. An address scoring 85 on a catch-all domain is very likely valid. One scoring 15 is likely fabricated. This distinction is worth significant revenue in B2B outreach.
Can VeriMails verify self-hosted email servers?
Yes. VeriMails verifies any domain with valid MX records, including self-hosted servers running Postfix, Exchange, Zimbra, or other mail server software. Self-hosted servers have varied configurations, so results depend on the specific server setup.
What's the accuracy for Microsoft 365 catch-all domains?
Microsoft 365 catch-all domains are our strongest catch-all scoring scenario because corporate naming conventions (firstname.lastname@) are highly predictable. Expect high-confidence scores for addresses following the organization's established pattern.
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