Instantly describes its verifier as a step you run: you upload your list, and it returns a report you can load into your outreach. The labels are valid, invalid and a shared risky-or-unknown result for addresses whose status is uncertain (instantly.ai/email-verification, read 24 September 2026). The check happens when you ask for it, on the list you give it.
That shared bucket holds two different problems. A catch-all domain answered 250 for every address, so the mailbox can't be confirmed by anyone. An unknown result means the server gave no usable answer, often a temporary block or greylisting. You'd treat them differently: catch-all goes to a test batch, and unknown gets a re-check next week.
Cold email puts a lot of weight on that split. Your warmed sending domains took weeks to build, and around 28% of a B2B list sits on accept-all domains. Sending that whole segment as though it were confirmed is how a healthy domain picks up hard bounces.
ZapBounce returns four results, valid, invalid, catch_all and unknown, with role and disposable flags on top. We get them from our own SMTP check on port 25, closed before DATA, so nobody receives an email. Verify the lead file before it reaches Instantly, then load valid into your main campaign and catch_all into a smaller one. The Instantly guide covers the upload.
Pricing fits outbound volume. You pay $5 for 1,000 checks or $139 for 100,000, and credits never expire. Unknown results and duplicates are never billed, so a re-check that comes back unknown again costs you nothing. See the full ladder on the pricing page.
Related questions
Is Instantly's email verification enough for cold email?
Instantly's verification is a quick first pass inside the tool you send from. Before a large campaign, split its risky-or-unknown result into catch-all and unknown with an independent SMTP check. At ZapBounce that costs $5 per 1,000 addresses, and unknowns are free.
Should I send to risky emails in Instantly?
Send risky addresses only in a separate, smaller campaign on a mailbox you can afford to test. Around 28% of a B2B list sits on catch-all domains, and no address on those domains can be confirmed at mailbox level before the send.
Should I verify before or after uploading to Instantly?
Verify before the upload. A list already inside Instantly is one launch away from your warmed domains. A check at the source lets you build separate campaigns by result from the start.
Does verification touch my Instantly sending mailboxes?
ZapBounce checks from its own servers, not from your sending mailboxes. The connection closes before any message data, so your Instantly domains and their warmup stay untouched.