Email subdomain to root domain: match mail.acme.com and acme.com as one company
In short: Upload a list and get a root_domain column that strips subdomains (mail.eu.acme.com becomes acme.com, and acme.co.uk stays whole), plus a count of addresses for each company domain. Limit: It uses a short built-in list of two-part endings, not the full public suffix list.
Upload a CSV or .xlsx file, or paste it with a header row and an email column. Each address gets a root_domain column: the part of the domain a company registers, so mail.eu.acme.com becomes acme.com and uk.initech.co.uk becomes initech.co.uk. You also get the addresses counted for each root domain, and both files to download.
Price: this tool is free. Checking a whole email list is from $9/mo, and the first 100 checks are free with Google, no card. Check your list free nowSee pricing
Sample result
Six example addresses on 6 mail domains belong to 5 root domains: mail.acme.example joins acme.example, and uk.initech.co.uk joins initech.co.uk.
- Root domains
- 5
- Mail domains
- 6
- Rows read
- 6
What this means for you
Matching companies does not show which mailboxes work; a check shows which addresses exist.
- Subdomains stripped
- co.uk and com.au kept whole
- Counts per company
- Original email untouched
- Domains
- Company match
- CSV
By SimpleVerifier Team · Last updated · Runs in your browser; nothing you paste is sent to us
Matched the companies?
- Download the list, or use the check button under the result, which carries its addresses across.
- Upload or paste it at /verify. Every address gets a live mailbox check, and the first 100 email checks are free with a Google sign-in, no card.
How do I turn email subdomains into root domains?
- Upload the file as a CSV or .xlsx, or paste the cells with the header row first.
- The email column is found by name or by its contents.
- Read the root domains and how many addresses each has.
- Download the list with root_domain added, or the counts.
Example
- You enter
- Six rows with addresses on mail.acme.example, acme.example, eu.sales.globex.example, initech.co.uk, uk.initech.co.uk and gmail.com.
- You get
- root_domain added to every row: acme.example (2 addresses), globex.example, initech.co.uk (2 addresses) and gmail.com. 3 addresses were on a subdomain, and 6 mail domains become 5 root domains.
- Limits
- Runs in your browser with no row cap; an uploaded file can be up to 25 MB. Nothing is uploaded.
Why do subdomains matter on a lead list?
Some companies give staff addresses on a subdomain, such as jane@eu.acme.com or jane@mail.acme.com. A tool that groups by the text after the @ sees three companies where there is one, so a cap of one contact per company, or a suppression of a customer's domain, misses them.
With a root domain column you can dedupe, count or suppress by company. Use it with limit contacts per company or remove emails by domain.
How is the root domain found?
Normally the last two parts of the name: sales.acme.com becomes acme.com. For endings that have two parts, such as co.uk or com.au, the last three are kept, so uk.initech.co.uk becomes initech.co.uk rather than co.uk.
The tool carries a short built-in list of common two-part endings. It is not the full public suffix list, so an unusual ending may be cut one part too far; check the counts table for names that look wrong.
What about Gmail and other personal mail?
Addresses on gmail.com, outlook.com and similar are already at their root, so they stay as they are. Two people on gmail.com are not one company, so treat webmail separately: the free vs business email filter splits them out first.
Everything runs in your browser; the file is never uploaded.
Who uses this tool, and for what?
- Cold emailers
- Cap contacts per company properly when some staff use subdomain addresses.
- Sales teams
- Match a lead list to existing customers by company domain, not by exact mail domain.
- Agencies
- Count how many people at each company a list holds.
What can’t this tool tell you?
- It uses a short built-in list of two-part endings, not the full public suffix list.
- A company with several unrelated domains (a parent and a brand) is not joined; only subdomains of one name are.
- It does not check whether the domain has a mail server or website.
- It does not check whether an address exists.
Common questions
- Does it look anything up?
- No. It works on the text of the address only, so it is instant and nothing leaves your browser.
- Does it work for co.uk and com.au?
- Yes, for the common two-part endings in its built-in list. It is not the full public suffix list.
- What if the address has no readable domain?
- The root_domain cell is left blank and the row count is shown above the table.
- Is the original domain kept?
- The email column is untouched. A subdomain_removed column shows what was cut off.
- Can I paste instead of uploading?
- Yes. Pasted CSV text works the same as a file, and .xlsx files are read too.
- Is my list uploaded?
- No. The file is read in your browser and nothing is sent anywhere unless you choose to check the addresses afterwards.
A tidy list can still be full of dead addresses.
Extracting, deduplicating and syntax checks all work on the text of an address. None of them can tell whether the mailbox exists. Only the server that hosts it can answer that, through an SMTP check, and that is what the paid product does.
- Upload the cleaned file as it is: CSVs up to 100,000 rows
- A real SMTP mailbox check on every row, with catch-all detection
- Small list? Starter at $9/mo covers 2,500 emails a month, cancel anytime
Plans from $9 a month, cancel anytime, no contract. Sign in with Google and your first 100 email checks are free, no card. The free tools stay free either way.