ESP matching: split a lead list into Google, Microsoft and other files
In short: Looks up every lead's mailbox provider from MX and SPF, gives you one CSV for Google, one for Microsoft and one for everything else, and works out how many days each group takes from your inboxes. Limit: It says where mail goes, not whether the mailbox exists.
ESP matching means sending to Google-hosted leads from Google Workspace inboxes and to Microsoft-hosted leads from Microsoft 365 inboxes. Paste a lead list or upload a CSV: every domain's MX record (and SPF behind a gateway) puts each row in Google, Microsoft or other. Download one file per group, with your columns kept, and see how many days each takes from your inboxes.
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. See pricing
Sample result
700 Google, 400 Microsoft and 100 other leads, each in its own file.
- Leads split
- 1,200
- 700
- Microsoft
- 400
What this means for you
Send each file from inboxes on the same provider: 3 days for Google, 2 for Microsoft at 300 a day.
- Google, Microsoft, other
- Read from MX, SPF behind gateways
- One CSV per provider
- Days from your inbox count
- Instantly
- Smartlead
- CSV
By SimpleVerifier Team · Last updated
Matched by provider. Now, which leads would bounce?
- A bounce costs a Google or a Microsoft inbox the same, so check the addresses before the campaigns start.
- Upload each file at /verify for a live mailbox check on every row, up to 100,000 rows a file.
- The first 100 email checks are free with a Google sign-in, no card.
How do I split a lead list for ESP matching?
- Paste the leads or upload the CSV from Apollo, Clay or your CRM, up to 5,000 rows; the email column is found for you.
- Enter how many Google and Microsoft sending inboxes you have and how many cold emails each sends a day.
- Press Split by provider. Only the unique domains are sent for the DNS lookup; the rows stay in your browser.
- Download the Google, Microsoft and other files and load each into its own campaign in Instantly, Smartlead or lemlist.
Example
- You enter
- 1,200 leads: 700 at domains on Google Workspace or Gmail, 400 on Microsoft 365 or Outlook.com, 100 elsewhere; 10 Google and 10 Microsoft inboxes at 30 cold emails a day each.
- You get
- Three files: Google (700), Microsoft (400) and other (100). The first email takes 3 days for Google leads (700 ÷ 300 a day), 2 for Microsoft (400 ÷ 300) and 1 for other leads from both pools (100 ÷ 600).
- Limits
- Up to 5,000 rows and 1,000 unique domains a run; only the domains are sent for the MX and SPF lookup.
What is ESP matching in cold email?
A practice from cold email: mail sent from a Google Workspace inbox to a Gmail or Workspace recipient stays inside Google, and Microsoft to Microsoft stays inside Microsoft, so teams split their lead list by the recipient's provider and send each part from inboxes on the same one. Sequencers such as Instantly and Smartlead let you pick the sending inboxes per campaign, so the split is done before import, one file per provider.
The provider is read from the domain's MX record, not the address: [email protected] is a Google lead when acme.com's MX points at aspmx.l.google.com. Behind a security gateway such as Proofpoint, the SPF record decides when it names exactly one of Google and Microsoft; otherwise the row goes to other. The same lookup runs in the bulk email provider lookup; this tool adds the per-provider files and the sending plan.
How many days will each group take?
Days = leads in the group ÷ (inboxes on that provider × cold emails per inbox a day), rounded up, for the first email of the sequence. Other-provider leads can go from either pool, so they're counted against both together. Most cold email setups keep each inbox to a few dozen a day; the cold email volume calculator works out how many inboxes a target volume needs.
How is this different from splitting by the domain name?
| This tool | Filter by @gmail.com / @outlook.com | |
|---|---|---|
| Company domains on Google Workspace | Missed | |
| Company domains on Microsoft 365 | Microsoft | Missed |
| Domains behind a gateway | From SPF, where it shows | Missed |
| Domains with no mail server | Set aside | Kept |
Who uses this tool, and for what?
- Cold emailers
- Load Google and Microsoft leads into separate Instantly or Smartlead campaigns with matching inboxes.
- Agencies
- Size how many Google and Microsoft inboxes a client's list needs before buying them.
- Sales ops
- Add a provider column to the CRM export so routing rules can use it.
What can’t this tool tell you?
- It reads DNS, so it says where mail goes, not whether the mailbox exists.
- Behind a gateway, the provider comes from SPF and can be wrong when a company sends from one provider and receives on another.
- The days figure covers the first email only, at the volume you enter.
- One run takes up to 5,000 rows and 1,000 unique domains.
Common questions
- What is ESP matching?
- Sending to each lead from an inbox on the same mailbox provider: Google leads from Google Workspace, Microsoft leads from Microsoft 365. This tool does the split for a whole list.
- How do I know if a lead uses Google Workspace or Outlook?
- Read the MX record of the domain after the @. Hosts at google.com or googlemail.com are Google; hosts at outlook.com or protection.outlook.com are Microsoft 365. Paste the list here and every row is labelled.
- What goes in the other file?
- Yahoo, Zoho, Proton, GoDaddy and every unrecognised mail host, plus gateway domains whose SPF doesn't name exactly one of Google and Microsoft. Send them from whichever pool has room.
- Does ESP matching guarantee the inbox?
- No. It's one of several things senders do; list quality, warm-up and copy matter as much. A list with dead addresses still bounces whatever inbox sends to it.
- Are my leads uploaded?
- No. The CSV is read in your browser and only the unique domains are sent for the DNS lookup. Nothing is stored.
Sources
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.