In this article
How does email lookup work?
There are three steps, and good tools do all of them. Pattern inference takes a name and a company domain and generates the likely address, such as firstname.lastname at the domain. Database matching checks that name and domain against a stored index of known addresses. Verification asks the receiving mail server whether it would accept the address, without sending a message. [7]
Databases are large and vendor-reported. Hunter's home page counts more than 150 million email addresses verified, and Apollo's says it holds more than 240 million contacts. [1][2] Both are marketing figures from the vendors and neither says how current they are, so do not read size as accuracy.
A server check has a known blind spot. An accept-all (catch-all) domain says yes to any address, so the check cannot tell a real mailbox from a made-up one. Hunter found that about 38% of the 2,572 domains in its sample were accept-all. [7]
How accurate are email finders?
The only independent-style comparison we found is a 2026 benchmark by Anymail Finder, a competitor that ranks first in its own test. It looked up 5,000 decision-makers from LinkedIn Sales Navigator in the US, UK, France and Germany. It collected the results on 19 June 2026 and judged each address valid by a panel of three verification services. It was not a live send. [3]
Hunter found an address for 57.6% and Apollo for 68.1%. Among the addresses returned, 86.1% of Hunter's and 91.3% of Apollo's were valid. [3] So Apollo's estimated bounce rate in that test was 8.7%. [3] The figures we have often seen quoted, a 60 to 80 percent find rate and a 5 to 15 percent bounce on unverified lists, are not stated by any vendor page we could open, so we do not use them.
| Tool | Returned an address | Valid among those returned |
|---|---|---|
| Hunter | 57.6% | 86.1% |
| Apollo | 68.1% | 91.3% |
We also could not find a published, sourced split of how often companies use each email format. Formats vary by company. Guess one only when you have a verified example from the same domain.
What bounce rate is too high?
No one agrees on a single number. Google's sender guidelines say to keep the spam rate in Postmaster Tools below 0.3%, and Yahoo's say the same and ask senders to remove invalid recipients promptly. [4][5] Neither gives a bounce threshold. Mailgun says a bounce rate under 2% is generally considered acceptable. [6]
| Source | What it says | What it measures |
|---|---|---|
| Google, sender guidelines | Keep spam rate below 0.3% | Spam rate in Postmaster Tools, not bounces |
| Yahoo, sender best practices | Spam rate below 0.3%; remove invalid recipients promptly | Spam rate, not bounces |
| Mailgun | A bounce rate under 2% is generally acceptable | Bounce rate |
| Hunter's own test | Accept-all addresses bounced 27%; valid addresses 1% | Bounce rate by verification result |
So treat 2% as a sensible ceiling and anything near the 8.7% that Apollo's returned addresses showed in the Anymail test as a list that needs verifying. The cost of a bad list is not the bounce itself. It is what mailbox providers learn about your domain.
Is it legal to email business contacts?
In the US, the CAN-SPAM Act covers business email. The FTC's guide says the law makes no exception for business-to-business email. [8]
In the EU, GDPR defines personal data as any information relating to an identified or identifiable person [9], and a work address that names a person fits that description. We could not open the UK regulator's guidance on corporate subscribers, so we do not state the UK rules here. Check them, and the rules of each country you send to, before you send.
Why we judge before we look anyone up
Looking up an address is cheap, but sending to the wrong person costs you, because a bounce or an ignored message teaches mailbox providers something about your domain. We do the cheap judgement first, so the lookup list is short.
In our run of 19 October 2026, 1,635 new posts were judged and 70 kept: 49 worth a look and 21 ready to contact. The whole run cost $5.23, which is about 25 cents for each ready lead. The cost ladder is in the cost of one contact-ready lead.
What to do when no address turns up
Skip the contact, find another person at the same company, or reach the person on a channel that does not need the address. A company-wide address such as hello@ may reach a shared inbox instead of the person you want. We have no data on how often.
Whichever you choose, verify any address you did not build yourself, and check the bounce rate and the reply rate together after your first send. A high bounce rate points at the list. A low reply rate on a clean list points at the message.
Common questions
How do I find someone's work email address?
Guess the format from their name and the company domain, or look them up in an email database, then verify the result with a server check before sending. Use a verified address from the same company to confirm the format first.
How accurate are email finders?
In Anymail Finder's 2026 benchmark of 5,000 decision-makers, Hunter returned an address for 57.6% and Apollo for 68.1%, and 86.1% and 91.3% of those were valid. The publisher is a competitor and ranks first in its own test, and it was not a live send. [3]
What is an accept-all or catch-all domain?
A domain whose mail server says yes to any address, so a server check cannot tell a real mailbox from a made-up one. Hunter found about 38% of the 2,572 domains it sampled were accept-all, and accept-all addresses bounced 27% of the time against 1% for valid ones. [7]
Sources and further reading
- Hunter: find and verify professional email addressesHunterBack to text
- Apollo.io: the B2B database and sales platformApolloBack to text
- Email Finder BenchmarkAnymail FinderBack to text
- Email sender guidelinesGoogleBack to text
- Sender best practicesYahooBack to text
- Bounce rateMailgunBack to text
- Email verification guide: accept-all and catch-all domainsHunterBack to text
- CAN-SPAM Act: A Compliance Guide for BusinessFederal Trade CommissionBack to text
- Art. 4 GDPR: DefinitionsGDPR-info.euBack to text
