Best practices

Split traffic 50/50, measure completed-signup rate, bounce rate on subsequent sends, and 30-day engagement on each cohort. Run for at least two weeks at meaningful volume. Verification almost always wins on long-term metrics even when short-term conversion dips slightly.

Leave VEC's bulk-upload dedupe toggle on (default), normalize Gmail dot- and plus-aliases in your source, and cache verification results in your own database to skip re-checks of recently verified addresses.

Count unique addresses after deduplication, add 5% padding for retries and edge cases, and buy a PAYG tier that covers it with a single purchase. PAYG never expires, so over-buying the campaign is cheap insurance.

Split the results CSV into four cohorts: send (safe), drop (invalid + disabled + spamtrap + disposable), conditional (catch_all + risky + role + inbox_full), and refunded (unknown). Decisions on the conditional cohort depend on campaign goals.

Call the verify-single API on form submit to catch typos and disposables, then fire your double opt-in confirmation email only on addresses that passed verification. Two layers cost slightly more per signup but block 95%+ of bad addresses.

Every 30 to 60 days for active marketing lists, 90 days for slow-moving B2B databases, never for transactional-only contact stores. The right cadence balances credit cost against the rate at which clean addresses go stale.

Call the verify-single endpoint server-side on form submit, block obvious failures (invalid, disposable, disabled), warn on borderline statuses (risky, role), and let safe addresses through silently. Real-time at the form catches bad data before it pollutes your list.

Pair a Monthly plan sized to your normal volume with auto-refill on Balanced timing (5-minute delay), set the trigger threshold at 10 to 15% of your monthly grant, and pick a refill tier large enough to absorb a typical spike. Steady volume should rarely touch PAYG.

Keep catch-all results for warm B2B audiences and known-good corporate domains. Drop them for cold outreach and on consumer lists. Expect bounce rates of 5 to 20% if you do send, so isolate them in a separate segment with its own monitoring.

Drop role addresses (info@, support@, sales@) for cold marketing and B2C campaigns. Keep them for transactional mail, support replies, and warm B2B follow-ups where the team inbox is the intended destination.

Double opt-in (confirm via email link) builds higher-quality lists but loses 20 to 40% of signups. Single opt-in (no confirmation) grows the list faster but admits typos and abuse. Real-time verification on the form lets you get many of the benefits of double opt-in without the friction.

Always one key per environment. Separate keys for production, staging, development, and any ad-hoc scripts let you revoke one without breaking everything else, attribute usage clearly in Credits History, and contain the blast radius of a leaked key.

One shared Valid Email Checker account with team members is almost always the right call. Per-brand accounts only make sense if billing must be siloed by entity or if brands have legally separate ownership. Sharing pools credits, simplifies admin, and keeps reporting unified.

Real-time at signup keeps the list clean from day one and blocks bad data at entry. Batch later is cheaper if you accept lots of low-intent signups. Most teams should do both: real-time at the form for hard fails, batch refresh every 30 to 60 days.

Always verify first. Sending without pre-verification leaks bounces into your sender reputation, gets you flagged at the receiving ESPs, and burns deliverability that takes weeks to rebuild. Verification cost is a tiny fraction of the campaign damage from skipping it.

Trust that Unknown results never cost a credit, retry them on a separate schedule (24 to 48 hours later, lower priority), and never block real users on an Unknown result. The refund is automatic and reflected in Credits History.

Export your list, deduplicate, upload to VEC bulk, wait for completion, then download and segment by status before importing back to your ESP. The full pre-campaign cycle takes under an hour for most lists.

Add team members for everyone on the same business sharing the same credit pool. Open a second account only if billing must be separated by legal entity or if compliance forbids data sharing. Sharing credits is almost always more cost-efficient than running two accounts.

Switch when your PAYG spend across two or three consecutive months crosses the price of a comparable Monthly tier. Monthly plans cost less per credit at steady volume, and the auto-renewal removes the per-purchase friction.

Reduce bounce rates, protect your sender reputation, save money, improve deliverability, stay compliant. The case for treating email verification as essential, not optional.