How to verify an email list before a campaign

The fastest way to end up in spam is to send a campaign to a list you did not verify. Every address that does not exist bounces, every bounce counts against your domain, and after a few percent of them the mail providers stop trusting anything you send. The damage lands on your good addresses too.

Verifying a list before the first send is the cheapest deliverability work you will ever do. This guide explains what a verifier checks, how to read the results, and a routine for cleaning a list of any size.

What a hard bounce is, and why it matters

A hard bounce is a message rejected permanently, almost always because the mailbox does not exist. A soft bounce is a temporary rejection: a full mailbox, a server that is down, a message that is too large.

Mail providers watch your hard bounce rate closely. It is one of the clearest signals that a sender is emailing addresses they did not collect properly. Once the rate climbs past a low threshold, Google and Microsoft start routing your mail to spam, and a warmed domain can lose months of reputation in a single afternoon.

The invalid addresses in a list come from three places: typos, people who have changed jobs, and guessed addresses. All three are caught by verification.

What an email verifier checks

A proper verifier does more than check that an address looks like an email. The LeadVector Email Verifier runs four checks in order:

1. Syntax and disposable domains. Malformed addresses and throwaway domains are rejected before anything else runs.

2. DNS and MX records. Does the domain exist, and does it publish mail servers? A domain with no MX records cannot receive email.

3. Provider and gateway detection. Is the mail handled by Google Workspace, Microsoft 365, or a security gateway in front of them? This decides how the next check is done.

4. SMTP handshake. The verifier connects to the mail server and asks whether the specific mailbox exists, without sending a message.

The result is a status you can act on rather than a guess.

Reading the results

• Valid. The mail server confirmed the mailbox exists. Send.

• Invalid. The mail server said the mailbox does not exist, or the domain cannot receive mail. Remove before sending.

• Catch-all. The domain accepts mail for any address, so the server cannot confirm whether this specific mailbox exists. The address may be fine or may bounce. Treat catch-all addresses as a separate segment: send to them from a mailbox whose reputation you can afford to test, or only when the contact came from a reliable source.

Some verifiers hide catch-all inside "valid" to make their accuracy look better. Insist on seeing it separately.

A five-step routine for cleaning a list

1. Deduplicate. Same address twice means two bounces from one bad record, and two emails to one person if it is good.

2. Verify in bulk. Upload the CSV or XLSX to Bulk Search, map the email column, and run the verifier across every row. A list of a few thousand rows finishes in minutes.

3. Remove invalids. Export the results and drop every row marked invalid. Do not keep them "just in case".

4. Segment catch-alls. Move catch-all rows to their own list. Send to them later, in smaller batches, and watch the bounce rate.

5. Import the clean list into the campaign. LeadVector campaigns import leads from a list, so the path from verified spreadsheet to first send has no manual copying in the middle.

Verification results are kept on the contact for thirty days, so re-checking the same address inside that window is free.

When to verify

• Before the first send to any list, whether you built it, bought it, or exported it from a CRM.

• Before re-activating an old list. People change jobs. A list that was clean a year ago is not clean now.

• On every new address that enters a sequence. Addresses found through the LeadVector Email Finder or the Chrome extension arrive already verified. Addresses from forms, signatures, and spreadsheets do not.

Verification is not warmup

A verified list stops bounces. It does not make a new mailbox trusted. If the mailbox you are sending from is new, or has been idle, warm it up before the first campaign as well. Verification protects the list; warmup protects the sender. You need both.

Frequently asked questions

How many emails can I verify at once?

Whole spreadsheets through Bulk Search. Single checks run in the app, and every check is available through the API and the CLI.

Does verifying an email send a message to the address?

No. The SMTP handshake asks the server whether the mailbox exists and disconnects. The recipient sees nothing.

What bounce rate is safe?

Keep hard bounces under two percent of sends, and aim for well under one. Above that, expect deliverability to fall quickly.

Should I send to catch-all addresses?

Only from a mailbox whose reputation you can afford to risk, in small batches, and only when the address came from a source you trust. Never mix a large catch-all segment into a campaign with your best list.