Free tool
Email list cleaner and sending plan for lead lists
10,000 leads on a 3-step sequence need 55 mailboxes on 11 domains to go out in a month.
Sending plan for 10,000 leads
One mailbox starts about 183 new leads a month at 25 cold emails a working day and 3 emails per lead. Plan 14 days of warmup and a week of ramp: full volume from day 21.
55 mailboxes on 11 domains with warmup and the sequencer: import the clean CSV into a campaign and send from them.
Create 55 mailboxesAbout this tool
About the email list cleaner
That is 30,000 cold emails at 25 per mailbox a working day. Drop your CSV above to plan the leads that are left after cleaning: the tool removes duplicates, invalid and empty addresses, role addresses such as info@ and sales@, and free-mail if you sell to companies.
It also counts contacts per company, checks the mail servers of the biggest recipient domains, and gives you the clean file to download. The plan prices the mailboxes at $2.50 each a month with warmup and the sequencer included. The file is read in your browser and never uploaded.
How it works
What the cleaner checks
It reads the header row and finds the email, first name, company and website columns by their names and values; change any of them if the guess is wrong. Then every row gets one verdict:
- Invalid or empty: no address, or one that breaks email syntax (spaces, two @ signs, no domain ending); it would bounce or be skipped by the sequencer
- Duplicates: the same address twice, compared without case and spaces; the first row is kept
- Role addresses: shared inboxes such as info@, sales@, support@, hello@, office@ and admin@; nobody owns them, several people read them and they report spam more often
- Free-mail: Gmail, Yahoo, Outlook.com, iCloud, Proton and other consumer providers; remove them for a B2B list, keep them if you sell to consumers or freelancers
- No first name: rows that would open with an empty greeting if your copy uses the first name
- Contacts per company: rows per recipient domain, and the companies with more than 3 contacts; cap them at 1, 2, 3, 5 or 10 per company
- Mail server: an optional MX lookup of the 20 company domains with the most contacts, over Cloudflare's public DNS-over-HTTPS; domains without one cannot receive email
Background
How many mailboxes a lead list needs
Multiply the leads by the emails each lead gets (the first email and the follow-ups), divide by the working days you want to send in, and divide by 25 cold emails per mailbox a day. Put up to 5 mailboxes on each domain. One mailbox starts about 183 new leads a month on a 3-step sequence. Plan 14 days of warmup and a week of ramp before the list goes out at full volume.
Sent in one month (22 working days) on a 3-step sequence, the minimum order is 12 mailboxes:
- 1,000 leads: 3,000 emails, 12 mailboxes on 3 domains, $30 a month
- 5,000 leads: 15,000 emails, 28 mailboxes on 6 domains, $70 a month
- 10,000 leads: 30,000 emails, 55 mailboxes on 11 domains, $137.50 a month
- 25,000 leads: 75,000 emails, 137 mailboxes on 28 domains, $342.50 a month
- 50,000 leads: 150,000 emails, 273 mailboxes on 55 domains, $682.50 a month
- 500,000 leads: 1,500,000 emails, 2,728 mailboxes on 546 domains, a volume price on a call (1,000 mailboxes and up)
Background
From the clean file to the first send
Run the clean CSV through an email verifier: it asks the receiving servers whether each mailbox exists, which no file check can do, and flags catch-all domains that accept every address. Keep the bounce rate under 2%; if a campaign already bounces, why the bounce rate is too high sorts bad addresses from blocks, and how to pick an email verification program compares the options.
Then import the file into an Outreach2day campaign or your own sequencer. Exporting the list: Apollo, Clay, or any CSV with the column mapping. To size a volume instead of a list, use the cold email capacity calculator; to compare the monthly cost with other stacks, the cold email cost calculator.
The same rules as a file for Claude or ChatGPT, with kept and dropped files and a report: the lead list cleaner skill.
Free guide19 min read
Send 100,000 cold emails a month
Domains and mailboxes you need, DNS, warmup, lists, copy and follow-ups, with a launch checklist, sent to your inbox.
Questions
How many mailboxes do I need for 10,000 leads?
55 mailboxes on 11 domains to send 10,000 leads in a month on a 3-step sequence: 30,000 emails over 22 working days at 25 a mailbox a day. Over two months it is half that; with fewer follow-ups, fewer still. Add 14 days of warmup before the first send.
Is my lead list uploaded anywhere?
No. The file is read and cleaned in your browser tab and the clean CSV is built there too. The optional mail server check sends only the domain names to Cloudflare's public DNS resolver; no address and no row leaves the page.
Does this tool verify email addresses?
No. It checks syntax, duplicates, role and free-mail addresses and the mail servers of the top domains. Whether a mailbox exists, catch-all domains and spam traps need an email verifier that talks to the receiving servers; run the clean file through one before you send.
Should I remove role-based emails from a cold email list?
Yes for cold email. Addresses like info@ and sales@ reach a shared inbox, rarely a buyer, and several people can report the same email as spam. The cleaner removes them by default; untick the option to keep them.
Should I remove Gmail and other free-mail addresses?
For a B2B list, usually yes: a personal Gmail address in a company export is often outdated, and a lead's work address is the one that matches your copy. Keep them if you sell to consumers, freelancers or very small businesses.
How do I remove duplicate emails from a CSV?
Drop the CSV on the cleaner. It compares addresses without case or spaces, keeps the first row of each address and removes the rest, then lets you download the clean CSV and a second file with every removed row and the reason.
Which CSV exports does it read?
Exports from Apollo, Clay, Sales Navigator scrapers and enrichers, ZoomInfo, Lusha and any other CSV with one lead per row and a header row. Comma, semicolon, tab and pipe separators and quoted fields are detected; save Excel files as CSV first. Up to about 100,000 rows run smoothly.
How many contacts per company should I email?
Two or three at a time is a common cap. Several cold emails landing in one company on the same day get compared and forwarded, and one person's spam report then counts against all of them. Cap the list per company in the cleaner, or spread the contacts over weeks.
In your AI assistant
Run the same checks in Claude or ChatGPT
Free SKILL.md files with the rules behind this tool. Install them in Claude or Claude Code, or paste them into ChatGPT, Gemini, Grok or Cursor.
Mailboxes, warmup and sending in one place
$2.50 a mailbox a month. DNS records are set for you, and every mailbox shows its warmup numbers from day one.
Deliverability call
Talk to our deliverability team
Book a call with the people who run our mailbox infrastructure. We look at your current setup and tell you what to change. Running 1,000+ mailboxes? We also quote a volume price below every vendor list price in our comparisons, warmup and sending included.
- Review your domains, DNS records and current inbox placement
- Size the setup: domains, mailboxes per domain and daily volume per mailbox
- Plan warmup and the move from your current provider or sequencer
- 1,000+ mailboxes: a volume price per mailbox for your setup
Free call
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