Sales engagement

Check carriers, phone numbers and email domains in Mixmax

Let a Mixmax rule post events to your endpoint and look up the carrier block behind a US phone number in each call event.

Why the data matters in Mixmax

Mixmax sits inside Gmail and records calls, replies and sequence steps against one contact, so a phone number with the wrong format or an odd area leaves call notes attached to a record nobody can reach. Teams that route work by region end up with sequences that fire at the wrong hour for a contact whose number was never read properly.

What LookValid checks

LookValid checks for Mixmax
Product	What it does here	Credits
Carrier Lookup (original carrier)	For a US number, returns the carrier originally assigned the number block, the state and the rate center, which gives a rough region for routing. A ported number still shows its first carrier.	1 credit per lookup (numbers outside the covered numbering plan areas are free)
Phone Numbering-Plan Validation	Normalizes the number to E.164 and returns the number type the numbering plan assigns, so call records carry one consistent format.	1 credit per valid number
Email Domain Check	Checks the domain of a contact address for mail servers and throwaway providers before it is added to a sequence. It cannot prove a mailbox exists.	1 credit per address checked
IP Intelligence	Returns location and network details for an address seen in your own logs, which helps place a visitor who opened a tracked link.	1 credit per lookup

Connect it in four steps

Sign up at LookValid and create an API key.
Store the key in the LOOKVALID_API_KEY variable of the endpoint that receives the Mixmax webhook action, and store the whsec_ signing secret Mixmax shows once when the action is created in a second variable used to check each delivery.
After the signature check passes, call the function with the phone number from the event: it posts to the carrier-lookup endpoint, returns null when no block is found and throws the error code and fix when the API refuses the call.
Save the state, rate center and line type hint on the contact record in your CRM, and respond with a 2xx status quickly so Mixmax counts the delivery as received.

the HTTPS endpoint a Mixmax rule posts to through its webhook action The call is POST https://YOUR_API_HOST/v1/carrier-lookup and costs 1 credit per lookup (numbers outside the covered numbering plan areas are free).

lookUpMixmaxCallNumber.mjs

1const API_URL = "https://YOUR_API_HOST/v1/carrier-lookup";
2
3export async function lookUpMixmaxCallNumber(value) {
4  const response = await fetch(API_URL, {
5    method: "POST",
6    headers: {
7      Authorization: `Bearer ${process.env.LOOKVALID_API_KEY}`,
8      "Content-Type": "application/json",
9    },
10    body: JSON.stringify({
11      "phone": value,
12    }),
13  });
14  const result = await response.json();
15  if (!response.ok) throw new Error(`${result.error.code}: ${result.error.fix}`);
16  if (!result.found) return null;
17  return {
18      "carrier_state": result.data?.state ?? null,
19      "carrier_rate_center": result.data?.rate_center ?? null,
20      "carrier_line_type": result.data?.line_type ?? null,
21  };
22}

Where each response field goes in Mixmax
Response field	Goes into
data.state	carrier_state
data.rate_center	carrier_rate_center
data.line_type	carrier_line_type

The recipe returns nothing when the lookup finds nothing, which costs no credits for this product, and stops with the error code and fix on a failed request.

Without code

A rule webhook action posts to any HTTPS address, so an automation platform with a generic HTTP request step can be the receiver without a dedicated app. Point the action at the platform catch URL, add a step that sends the phone number to the carrier-lookup endpoint with your key in a bearer header, and add a final step that writes the state and rate center onto the contact.

REST and MCPOne shared credit balance

Questions

How many credits does a carrier lookup use?

It draws credits from your LookValid balance. The pricing page lists the current amount for carrier lookups.

Does the result show who the carrier is today?

No. It shows the carrier originally assigned the number block, from public number-assignment reports. Canada and the Caribbean are not covered.

Where does the key go next to the Mixmax signing secret?

The LookValid key sits in LOOKVALID_API_KEY. The Mixmax signing secret is a separate value that only checks that a delivery came from Mixmax, so keep the two apart.

Sources

Mixmax Developer https://developer.mixmax.com/, read 2026-10-18
Mixmax Developer: rules and webhook actions https://developer.mixmax.com/reference/rules, read 2026-10-18
LookValid API reference: Carrier Lookup (original carrier) https://lookvalid.com/docs/api/carrier-lookup, read 2026-10-18

LookValid is run by Meralume Labs. It is not connected to, endorsed by or a partner of any company or product named on this page, and every product name belongs to its owner.

LookValid bills every lookup in credits from one shared balance, so the same key works for each check above.

See Carrier Lookup (original carrier)