22% of business email addresses go invalid every year. A list that passed verification 6 months ago has already drifted. This guide covers how email list cleaning services work, what results to expect, realistic pricing benchmarks, and when to clean your list vs. verify in real time.
A good email cleaning service runs each address through four sequential stages. Each stage eliminates a different class of bad addresses before reaching the expensive SMTP probe.
Confirms the domain exists and has valid mail exchange records. Eliminates typo domains (gnail.com, gmai.com) and dead domains instantly, before any SMTP connection.
Checks email format against RFC 5321 rules. Catches addresses with double @, invalid characters, or malformed local parts. Fast and done server-side before any network call.
Checks the domain against a continuously-updated list of 3,500+ disposable / temporary email providers (Mailinator, Guerrilla Mail, 10 Minute Mail, etc.). Prevents fake signups.
The service opens an SMTP connection and sends a RCPT TO command to simulate a delivery. The mail server responds positively (250) or negatively (550). No email is actually sent - just the probe.
| Result | Meaning | Action |
|---|---|---|
| valid | SMTP server confirmed the mailbox exists and can receive mail | Send - this is a real, deliverable address |
| invalid | Mailbox does not exist on the server (550 RCPT TO response) | Remove - sending will hard bounce |
| catch-all | Domain accepts all incoming email, making individual mailbox confirmation impossible | Use score to decide: high score (70+) = send, low score = suppress |
| disposable | Address belongs to a known temporary/throwaway email provider | Remove - not a real prospect; likely a fake signup |
| unknown | Verification inconclusive: server timed out, greylisted, or blocked probe IPs | Conservative: suppress for cold email; acceptable for warm email |
| Service | 1K emails | 10K emails | 100K emails | Credits expire? |
|---|---|---|---|---|
| BounceZero | $3 | $25 | $180 | Never |
| ZeroBounce | $8 | $40 | $290 | 1 year |
| NeverBounce | $8 | $50 | $300 | Never |
| Kickbox | $5 | $40 | $250 | Never |
| Emailable | $5 | $30 | $200 | Never |
| MillionVerifier | $3 | $15 | $79 | Never |
Email list cleaning tests each address to determine whether it can receive mail. A cleaning service runs DNS MX checks, SMTP handshake probes, disposable detection, and syntax validation. Results are classified as valid, invalid, catch-all, disposable, or unknown. Invalid and disposable addresses are removed before sending to protect sender reputation and reduce bounce rate.
Cleaning services charge $1-$8 per 1,000 emails depending on provider and volume. BounceZero charges $3/1K; NeverBounce and ZeroBounce charge $8/1K for small lists. At 100,000 emails the cost drops to $2-$4/1K with most providers. Pay-as-you-go credits that never expire are better than monthly subscriptions for teams that clean lists occasionally.
Cold outreach lists should be cleaned every time (business email changes at 22% annually). Newsletter lists should be cleaned every 3-6 months or whenever bounce rate exceeds 2%. CRM contacts should be cleaned quarterly. Newly purchased or scraped lists should always be cleaned before first contact.
Upload a CSV, get results in minutes. Valid, invalid, catch-all, disposable - one clean file ready for your sequencer. $3/1K. Credits never expire.
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