Bulk MX lookup: split an email list by Google, Microsoft and other
A bulk MX lookup reads the MX records of every domain in a list to see who receives its mail. Upload a CSV of addresses or domains and each row is labelled Google Workspace or Gmail, Microsoft 365 or Outlook, or another provider, using SPF where a gateway hides it. Yahoo, Zoho and Proton get their own groups. Filter the results, then download the split. For one domain in detail, use the email provider lookup.
Sample result
Google Workspace runs email for acme.example; Microsoft 365 for yourcompany.example.
- Mail provider
- Google Workspace
- Domain
- acme.example
- MX host
- aspmx.l.google.com
What this means for you
Split your list by provider so you can match each one's sending rules and pace.
- Up to 5,000 rows and 1,000 domains a run
- Names the provider behind each domain
- Reads SPF for the host behind a gateway
- Download split into Google, Microsoft, other
- Bulk
- MX
- CSV
By SimpleVerifier Team · Last updated
How do I run a bulk MX lookup on a list?
- Paste addresses or domains, or upload a CSV of up to 5,000 rows and 1,000 unique domains; the email column is found for you. A column of domains or website URLs works too.
- Press Look up providers. The file is read in your browser, and only the unique domains are sent for a DNS lookup, 100 at a time.
- Read the split: Google, Microsoft, Yahoo, Zoho, Proton, other providers, and domains with no mail server at all. Click a group to filter the table.
- Download the filtered group, or the whole file with provider columns added to your original rows.
Example
- You enter
- A CSV of addresses whose domains include
acme.exampleandyourcompany.example. - You get
acme.exampleis grouped under Google (MX hostaspmx.l.google.com) andyourcompany.exampleunder Microsoft (MX hostyourcompany-example.mail.protection.outlook.com). Click a group to filter it, then download that group or your whole file with provider columns added.- Limits
- Up to 5,000 rows and 1,000 unique domains a run, and 1,000 domains per ten minutes per connection. Some visitors without an account get the first 25 rows and sign in with Google for the rest.
What is an MX lookup, and how are rows grouped?
An MX lookup asks DNS for a domain's mail exchanger records, which name the servers that receive its mail (RFC 5321). Hosts ending in google.com or smtp.goog are Google (Workspace, or Gmail for gmail.com); hosts ending in mail.protection.outlook.com are Microsoft 365, and olc.protection.outlook.com is Outlook.com. About 40 other providers, gateways and forwarders are named using the rules from our study of email providers at large companies.
When the MX points at a security gateway such as Proofpoint or Mimecast, the tool reads the domain's SPF record. If SPF includes Microsoft 365 and not Google, or the reverse, the row goes in that group and is marked "(gateway)"; otherwise it stays in Other. GoDaddy-hosted mail can be either Microsoft or Google, so it stays in Other too.
Why split an email list by provider?
So you can watch, pace and send to each big mailbox provider on its own terms. Gmail and Outlook judge your mail separately, publish their own sender rules and give you different reporting tools: Google Postmaster Tools and Microsoft's SNDS. Splitting a campaign by provider lets you see when one of them starts deferring or junking your mail, and slow down for that provider only. Cold senders also match inbox to recipient, sending to Google-hosted contacts from Google Workspace inboxes and Microsoft-hosted contacts from Microsoft 365. Our guide to segmenting by mailbox provider covers both.
The mix varies a lot by audience. In our provider study, 93.5% of 200 SaaS companies received mail directly at Google Workspace, while only 4.0% of S&P 500 companies did; 56.7% of the S&P 500 routed mail through a security gateway first.
How many domains can I check in one bulk MX lookup?
Up to 5,000 rows and 1,000 unique domains per run. Most lists have far fewer domains than rows, because many contacts share a company. Each connection can look up 1,000 domains per ten minutes. Lookups are DNS only, two queries per domain, and nothing is sent to the domains' mail servers.
The provider is a property of the domain, so every address at a working domain looks the same here: the employee who left in 2023 and the one who joined last week. A row in No mail server will bounce for certain; the rest need a mailbox check to tell real from dead. Verify the list before you send.
Is this faster than checking MX records one by one?
| This tool | `dig MX` per domain | |
|---|---|---|
| Domains per run | Up to 1,000 | One at a time, or a script |
| Provider named | Yes, for about 40 providers | You read the hostnames |
| Provider behind a gateway | Inferred from SPF | Another dig TXT per domain |
| Original rows kept with provider columns | Yes, as a CSV | You join the results yourself |
A shell loop does the raw part: while read d; do echo "$d $(dig +short MX $d | head -1)"; done < domains.txt.
Who uses this tool, and for what?
- Cold emailers
- Split a lead list into Google-hosted and Microsoft-hosted contacts so each group sends from matching inboxes, and drop the No mail server rows before they bounce.
- Marketers
- Segment a newsletter list by mailbox provider before a big send, so you can pace Microsoft and Google separately and spot which one is deferring you.
- Sales ops
- Add provider columns to an account list for routing and reporting, and find accounts behind Proofpoint or Mimecast, where verification often returns catch-all.
- Agencies
- Show a client the provider mix of their list before you plan a campaign, then check the gateway-heavy domains with the catch-all checker.
What can’t this tool tell you?
- It tells you who hosts a domain's mail, not whether any address there exists. Dead mailboxes at a working domain look the same as live ones.
- Behind a security gateway, the Google or Microsoft label comes from SPF and is marked "(gateway)": strong evidence, not proof.
- GoDaddy-hosted and unrecognised hosts land in Other.
- One run takes up to 5,000 rows and 1,000 unique domains; larger lists need several runs.
Common questions
- How do I do a bulk MX lookup?
- Paste a list of domains or email addresses, or upload a CSV, and press Look up providers. The tool looks up each unique domain's MX and SPF records and labels every row with its provider. You can download the results as CSV.
- What is an MX lookup?
- A DNS query for a domain's MX (mail exchanger) records, which list the servers that accept its email and their preference order. The hostnames usually reveal the provider, such as Google Workspace or Microsoft 365.
- Is this bulk MX lookup free?
- Yes, it's free and there's no card or payment. Short lists run without an account; for longer lists you may be asked to sign in with Google first, which is free too. One connection can look up 1,000 unique domains per ten minutes, so it stays fast for everyone.
- How do I segment an email list by Gmail and Outlook?
- Group the addresses by the provider that hosts their domain, read from MX records, not by the domain name: plenty of company domains are hosted on Google Workspace or Microsoft 365. This tool does that and gives you a download per group.
- What's the difference from the email provider lookup?
- The email provider lookup checks one domain in detail, showing every MX host, its priority and the SPF record. This tool runs a whole list and gives you the split as downloadable files.
- Are my email addresses uploaded?
- No. The CSV is read in your browser, and only the list of unique domains is sent to our server for the DNS lookups. Addresses, names and other columns stay on your device, and nothing is stored.
- What does "No mail server" mean?
- The domain publishes no MX record, or a null MX that says it accepts no mail. Mail to those rows will almost certainly bounce, so remove them before sending.
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? $9 one-time covers 2,500 emails, no subscription
One plan, 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.