How to Test an Email Address Without Sending an Email (Four Checks)

You test an address without sending by running four checks in order: syntax, MX record, SMTP probe, then a status lookup. Each one rules out a different failure. None of them alone proves a person reads that mailbox.

TL;DR

• Run syntax, MX and SMTP checks yourself in about 10 minutes, for free. Outbound port 25 is often blocked on laptops and cloud hosts.
• A LeadOcean lookup by email returns the status on record for that address. It spends 1 record when the address is found and 0 when it is not.
• Treat catch_all, untested and unknown as "not proven", not as "good".

Prerequisites

• A terminal with dig and openssl (or nc).
• A LeadOcean API key, stored as $LEADOCEAN_API_KEY. The free plan has 1,000 records for life, no card, and 5 requests a second.
• Placeholder address used below: jane.doe@acme.com. Swap in your own.

Step 1: Check the syntax

A syntax check catches typos and missing parts before you spend a network call. It cannot tell you whether the mailbox exists.

import re

PATTERN = re.compile(
    r"^[A-Za-z0-9.!#$%&'*+/=?^_`{|}~-]{1,64}"
    r"@[A-Za-z0-9](?:[A-Za-z0-9-]{0,61}[A-Za-z0-9])?"
    r"(?:\.[A-Za-z0-9](?:[A-Za-z0-9-]{0,61}[A-Za-z0-9])?)+$"
)

def syntax_ok(email: str) -> bool:
    return bool(PATTERN.match(email)) and len(email) <= 254

print(syntax_ok("jane.doe@acme.com"))   # True
print(syntax_ok("jane.doe@acme"))       # False

This is a pragmatic pattern, not a full parser for every legal address. For the rules, read what email address syntax is.

Step 2: Look up the MX record

If the domain has no MX record, mail has nowhere to go. One command answers it.

dig +short MX gmail.com | sort -n

Output from a run on 2026-10-21 (first three lines):

5 gmail-smtp-in.l.google.com.
10 alt1.gmail-smtp-in.l.google.com.
20 alt2.gmail-smtp-in.l.google.com.

An empty result means the domain cannot receive mail. A domain that returns nothing is a hard stop. Lowest number wins, so probe the host with the lowest priority first.

Step 3: Probe the mail server with SMTP

An SMTP probe opens a conversation with the receiving server and quits before the message body. It follows the commands in RFC 5321 (September 2026).

nc mx1.acme.com 25

Use the lowest-priority MX host of the address's own domain from step 2 (mx1.acme.com is a placeholder).

Then type these lines, one at a time:

HELO check.example.org
MAIL FROM:<check@example.org>
RCPT TO:<jane.doe@acme.com>
QUIT

Read the reply to RCPT TO:

Three limits to know. Many providers block port 25 from home and cloud networks, so the connection hangs. Some servers answer 250 for every address (a catch-all). Some throttle or blacklist IPs that probe often, which hurts your own sending reputation if you probe from your mail IP. Read what SMTP verification is before you run this at volume.

Step 4: Look up the status in LeadOcean

LeadOcean does not run a live probe when you call it. It looks the address up in its people data and returns the status on record. That makes it fast and safe at volume, and it means an address we hold nothing for returns a 404 and costs nothing.

curl -s -X POST https://api.leadocean.io/v1/people/enrich \
  -H "x-api-key: $LEADOCEAN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"email": "jane.doe@acme.com", "reveal_email": true}'

Send exactly one identifier per call. For a list, loop with a pause that keeps you under your plan's rate limit (5 requests a second on Free, 200 on Agency).

If you have no address yet, search first. Sizing a search is free:

curl -s -X POST "https://api.leadocean.io/v1/people/search?count=true&limit=1" \
  -H "x-api-key: $LEADOCEAN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"emailStatus": ["verified"], "jobLevel": ["VP"], "country": ["US"]}'

In Claude or another MCP client, the free leadocean_list_enum_values tool lists the status values, so you never guess a string.

What you get

The email status values the API accepts, from leadocean_list_enum_values on 2026-10-21:

verified          Deliverable
catch_all_valid   Catch-all, mailbox confirmed
catch_all         Catch-all domain
risky             Risky
unknown           Unknown
untested          Not yet checked
invalid           Undeliverable
role              Role address
disposable        Disposable address
spam_trap         Spam trap
abuse             Abuse / complainer
derived           Derived, not verified
none              No email

A lookup response has this shape (response shape from the API reference, placeholder values):

{
  "success": true,
  "data": {
    "contact_data": {
      "has_email": true,
      "email_status": "verified",
      "email_type": "work",
      "contact_emails": [
        {
          "email": "jane.doe@acme.com",
          "type": "work",
          "status": "verified",
          "verified_batch_date": "2026-09-20"
        }
      ]
    }
  }
}

How to act on it:

• Send: verified and catch_all_valid.
• Do not send: invalid, spam_trap, abuse, disposable.
• Use with care: risky, role (a shared mailbox such as info@) and derived.
• Not proven: catch_all, untested, unknown. untested means nobody has checked the address yet. It may be fine.

verified_batch_date is the date of the verification run. A null date means the check was not run by LeadOcean. Personal addresses are never tested by LeadOcean, so treat verified on a personal address as a lead to verify.

Troubleshooting

FAQ