How to Find Which Network Hosts the Mail for Each Address on a List
To find which network hosts the mail for an address, look up the MX records of the domain after the @, resolve the first mail server to an IP address and map that address to a network and ASN. The bulk email mail server network finder does that for every address in a pasted list or CSV, up to 100 unique domains a run (500 after a free Google sign-in).
It reads DNS only, it checks the domain, not the mailbox, and a security gateway shows its own network, not the mailbox provider's.
Why group a list by mail network
A name match on the MX host tells you the provider when it is a big one. The network goes further: the same IP-to-ASN lookup places a small hosting company's mail server, a university's or a regional ISP's, which no name list will cover. For a prospect list it is a way to cut the list into groups that share infrastructure, and to see which addresses sit on a handful of large networks.
The by-hand way
- Take the domain after the @, for example
acme.example. - Look up its MX records with the MX lookup and note the host with the lowest priority number.
- Resolve that host to an IP address.
- Look up the IP in an IP-to-ASN source such as Team Cymru's mapping to get the ASN and network name.
Doing that for a few domains is fine. For a list, bulk mail server lookup takes bare domains.
Step 1: paste the addresses
Paste addresses one per line, or upload a CSV. Only the unique domains are sent, never the mailbox names, 10 a request.
Step 2: run the check
Press Find mail server networks. MX, address, reverse-DNS and IP-to-ASN lookups all go over DNS. No mail server is contacted.
Step 3: read the result
Each row is labelled with the network of the first mail server, and carries the MX host, IP and ASN. Filter by network to split the list. Other rows are:
| Result | What it means |
|---|---|
| No mail server | No MX record, or a null MX (RFC 7505); the address will bounce |
| Network not found | The IP resolved but the ASN data does not name a network |
| Lookup failed | DNS did not answer in time; run the list again |
The row's note can also say a domain has only one MX host, that all its MX hosts are on one network, or that an address has no reverse-DNS name. Those describe the mail setup; they are not errors.
What this check cannot do
- It checks the domain, not the mailbox: a mail server on a well-known network can still reject an address.
- Only the first mail server is shown, and only the first three hosts are resolved to IPs.
- A domain behind a security gateway shows the gateway's network. Use the bulk email provider lookup to read past it, and how to verify emails behind security gateways for what that means for checking.
- Up to 100 unique domains a run without an account, 500 signed in.
For the provider name rather than the network, see how to check a prospect's email provider.
Next: the mailboxes
Use the verify page to find which mailboxes exist: the first 100 checks are free with a Google sign-in, no card.
Try it now
Paste your list into the bulk email mail server network finder.
Common questions
How do I find which network hosts the mail for an email address?
Look up the MX records of the domain after the @, take the first mail server, resolve it to an IP address and look the IP up in an IP-to-ASN database. A bulk email mail server network finder does that for every address in a pasted list.
Which mail server does the tool use?
The first MX host, the one with the lowest priority number. The row shows its host name, IP address, network and ASN.
Why does a company show a gateway's network?
Mail for a domain behind a security gateway reaches the gateway first, so its network is what the MX records point to. The bulk email provider lookup reads past gateways to the mailbox provider.
Does it connect to the mail server?
No. It reads DNS and IP-to-ASN data over DNS. It never opens a connection to a mail server.
Does the check tell me whether the mailbox exists?
No. It checks the domain, not the mailbox.
Check your list before you send
Real mailbox checks over SMTP, and nothing is sent to the address. Sign in with Google and your first 100 email checks are free, no card. Plans for bigger lists are on the pricing page.