Verify Email

Check whether an email address looks deliverable. The tool checks syntax, then DNS (MX, with an A/AAAA fallback), and can optionally probe SMTP up to RCPT TO. It never sends a message.

Warning: Authorised use only. SMTP probing talks to someone else's mail server. Use it only on addresses and domains you are allowed to test.

Install

Python 3.10 or newer. dnspython installs with the package.

pip install lupaxa-verify-email
verify-email --help

CLI

verify-email user@example.com
verify-email user@example.com --inspection 4 --from-address probe@yourdomain.example
verify-email --file emails.txt --inspection 3 --from-address probe@yourdomain.example
verify-email user@example.com --format json --output results.json
python -m lupaxa.verify_email --version

emails.txt is one address per line. Blank lines and lines starting with # are skipped. A leading UTF-8 BOM is ignored. A file with no addresses exits 2. During SMTP checks the tool waits 1 second between addresses in a file. --delay 0 turns that pause off. --delay is 0 for syntax and DNS checks.

An MX record names a host and has no port. Inbound delivery uses port 25. Pass --port when the server you want to probe is listening somewhere else. Port 465 is implicit TLS. Any other port starts in cleartext and upgrades when the server offers STARTTLS. The probe does not verify the certificate. If the handshake fails, that host is skipped.

Unicode domains are looked up as A-labels. A Unicode local part is sent with SMTPUTF8 when the server advertises it. If the server does not, the result is unknown.

--from-address is required for inspection levels 3 and 4. There is no default sender. RCPT TO is only trusted after MAIL FROM returns 250. A 4xx on MAIL FROM is treated like a 4xx on RCPT TO. Pass an address or --file, not both. Inspection must be 1, 2, 3, or 4. --debug writes the DNS and SMTP dialogue to stderr, so JSON on stdout stays intact.

CLI Flags

Exit Codes

Exit 1 is also used when the address file cannot be read, including a file that is not UTF-8. Exit 2 is also used when the file has no addresses, --from-address is missing for an SMTP check, the inspection level is outside 1–4, an address and --file are both set, --delay is negative, or the port or timeout is unusable.

Inspection Levels

Every run returns valid, invalid, or unknown. A null MX (0 .) or NXDOMAIN is invalid. A DNS timeout or SERVFAIL is unknown, so a resolver outage is not reported as a bad address.

252 means the server will accept the message without confirming the mailbox. Catch-all domains often answer that way, so levels 3 and 4 can report them as valid.

SMTP replies

The probe reads each reply until the final line, a status code followed by a space rather than a hyphen, and that line has arrived in full. It tries the next MX after a connection failure, a failed TLS handshake, a MAIL FROM rejection, or an unknown RCPT reply.

5.7.x is a policy or security refusal. It says the server would not complete the probe, which is different from a missing mailbox. The mailbox echoed in the reply is ignored, so spam-trap@example.com is not treated as a spam or block reply. A full mailbox stays valid at both SMTP levels, and result.ok is true, with the reason mailbox is full and cannot accept emails at this time.

Library

from lupaxa.verify_email import EmailValidator

validator = EmailValidator(
    inspection=3,
    from_address="probe@yourdomain.example",
)
result = validator.validate("user@example.com")
print(result.status, result.stage, result.reason)

validate always returns a ValidationResult. It does not raise for a bad address.

Some providers refuse mailbox probes. Those come back as unknown. A catch-all domain can look valid at levels 3 and 4. A Unicode local part is accepted at syntax and is probed only when the server offers SMTPUTF8.

Development

make init
make python-install-dev
make python-check