Before you send a cold email, check that the address is real. A quick manual look catches typos and dead domains, and an email verification tool checks with the receiving mail server whether the mailbox exists. Send only to addresses that pass, hold the "risky" ones back, and re-check any list that is more than a month or two old.

Here's the math that makes this worth the effort. Wes sends a first batch of 200 emails from his Gmail for a small consulting firm. Twelve bounce. That's 6 percent, and mailbox providers notice. A common rule of thumb among people who send mail for a living is to keep bounces well under 2 percent. At 6 percent, his next 200 emails are more likely to land in spam, including the ones to good addresses.

Why bad addresses hurt you

When you send to an address that doesn't exist, the receiving server sends back a bounce. Providers like Google and Microsoft watch how often your messages bounce, how often people mark them as spam and how often people reply or open them. High bounce rates suggest you're mailing a purchased or stale list, which is exactly what spammers do. Your reputation drops, and it follows both your domain and your sending address.

It's slow to climb back. For a small business sending from its own Gmail, a damaged reputation can quietly push even your ordinary customer emails to spam. That's the reason to be strict before the first send. Cold email deliverability basics covers the full picture, including the domain setup and warm-up.

Manual checks that cost nothing

Before any tool, read the list with your own eyes. It takes ten minutes for 100 addresses and catches a surprising amount.

  • Typos in the domain: gmial.com, outlok.com, a missing letter in the company name.
  • Role addresses such as info@, sales@, admin@, support@. These often go to a shared inbox that nobody reads, or to a spam filter. They're not invalid, but they rarely reach a decision maker.
  • Domains that don't match the company's website. If the site is redcanbrewing.example and the address ends in redcan-brewing.example, check which is right.
  • Duplicates and the same person listed twice with two addresses.
  • Old addresses for people whose profile now shows a new employer.

A spreadsheet trick helps: sort the email column by domain. Duplicates, typos and look-alike domains end up next to each other, and you can see in seconds when three people at one company have addresses in three different formats, which usually means one of them is a guess that needs checking. Then spot-check a few by visiting the company site and confirming that the person still works there and that the address pattern matches other staff addresses. How to find a business owner's email address covers patterns in more detail.

One thing not to do: don't send a test email to a guess just to see if it bounces. That's a bounce on your record, and it reveals your message to a stranger. A verifier does the same job without sending.

Verification tools and what they miss

An email verifier takes a list and returns a status for each address. Most check that the address is formatted correctly, that the domain exists and can receive mail, and then ask the mail server if the specific mailbox is accepted, without delivering a message. Many also flag disposable addresses, known spam traps and role accounts. Free options exist for a few checks at a time, and paid ones are priced per address or per batch.

Know what they miss. A tool can only report what the server tells it. Some servers refuse to answer, some answer "yes" to everything, and a mailbox can be valid today and full or closed next week. A verified address is a good bet, not a guarantee. Treat the result as "very likely to be delivered," and keep an eye on the real bounces from your first sends. Lead data you can check before paying suggests testing any provider on 20 addresses you already know before trusting it with 2,000.

Accept-all domains

Some company mail servers are set to accept any address at their domain, and sort out invalid ones afterward. Verifiers can't tell whether a specific mailbox exists on those, so they label the address "accept-all" or "risky." Small businesses on certain hosting setups do this a lot.

What to do with them? Don't throw them all away, because plenty are real. Instead, handle them carefully. If you have strong reason to trust the address (it's printed on the company's own website, or the person told you), send. If you guessed it from a pattern, send in a small batch of 10 to 20, watch for bounces over a day or two, and continue only if they come back clean. If you can reach the person by phone instead, call.

Verify again before a big send

People change jobs, companies close, and mailboxes get shut off. An address that was fine in March may bounce in June. If a list has been sitting for more than a month or two, run it through the verifier again before you send, even if you checked it when you built it. The cost is small compared with the cost of burning your sender reputation.

Also keep your own volume modest while you build trust: 20 to 50 emails a day per inbox when you start, increasing slowly. Google's published limits for regular accounts are much higher than what's safe for cold email. Send to your most reliable addresses first, so your early record looks healthy.

What to do with risky addresses

Sort your list into three groups: valid, risky and invalid. Send to valid. Drop invalid for good. For risky, choose a path: call instead, find the person on another channel, send a small test batch, or leave them out for now. Never mail a list of risky addresses all at once because a tool said "probably fine."

Also remove anyone who has bounced or unsubscribed from every future list, permanently. In the US, CAN-SPAM requires you to honor opt-outs promptly, and your email should include your physical address and a clear way to unsubscribe.

Keep a record of verified status

In your sheet, add two columns beside each email: "verified" (valid, risky, invalid) and the date. Add the source too. When you're debugging a bounce spike, those columns tell you in a minute which batch caused it. They also let you hand the list to someone else without a long explanation. If you're building a list from scratch, how to build a lead list has the six-column sheet to start from.

Rocketship's AI worker handles this on its own: it finds buyers by name with verified contact details, suppresses bounces, checks your sending domain before you burn it, and emails from your own Gmail at a sensible pace. Enrichment credits are tracked separately from leads; adding a person costs 1 credit, and a verified phone and email costs 5, charged only when found. Enrichment credits explained plainly walks through the numbers.

Clean data protects everything that comes after the send. Rocketship finds the buyers, emails them from your own Gmail, follows up, and books the meeting on its own. Plans that get you customers start at $24.99 a month (Launch), and every monthly plan starts with a 7-day free trial, card required. Answering your existing number is included; a dedicated line is $5 a month.