The only cat who can find existing email addresses by nickname.

From PyPI (recommended):

pip install mailcat-osint

From source:

git clone https://github.com/sharsil/mailcat
cd mailcat
pip install .

Run it with a username:

mailcat username

Or as a module:

python -m mailcat username

It's recommended to run mailcat through Tor or a proxy — see Routing through Tor below.

mailcat --tor username
proxychains4 -q mailcat username

mailcat username --proxy http://1.2.3.4:8080

You can check multiple usernames in one run.

Pass several usernames as positional arguments:

mailcat alice bob charlie

Or supply a file with one username (or email address) per line:

mailcat --file usernames.txt

File format example:

alice
bob@proton.me
charlie

You can also combine both — positional names are merged with those from the file:

mailcat alice --file more_users.txt

When more than one username is resolved, a header is printed before each result block so the output is easy to follow:

[*] Checking username: alice
...
[*] Checking username: bob
...

26 active providers covering > 158 domains (plus ~50 Posteo alias domains). Active checks run by default; deprecated checks remain in the source for revival but are skipped on a default run. See the comment block above each function in src/mailcat/__init__.py for the upstream change that broke it and notes on how to revive it.

Use -m or --max-connections if you get connection errors (Mailcat does 10 parallel connections max by default).

The SMTP-based checks (gmail, yandex, mailDe) reach the destination provider's MX servers on TCP port 25. Most residential ISPs and every major cloud provider (AWS, GCP, Azure, Heroku, …) block outbound port 25 as an anti-spam measure, so these checks will time out with messages like:

Error while checking gmail: Timed out connecting to gmail-smtp-in.l.google.com. on port 25

Tor exit nodes generally do not have port 25 blocked, which makes routing through Tor the easiest fix. Mailcat has built-in Tor support via the --tor flag — it expects a SOCKS5 proxy at 127.0.0.1:9050 (the default when you run tor locally).

# 1. Start Tor (macOS / Linux)
brew install tor && tor &        # macOS
sudo systemctl start tor          # Linux with systemd

# 2. Run mailcat through Tor — SMTP checks now succeed
mailcat alex --tor

# Or restrict to just the providers that need it
mailcat alex --tor -p gmail -p yandex -p mailDe

Tor adds ~5–15 s of latency per request, but it is the only reliable way to make the SMTP-25 checks work from a typical home or cloud environment. A clean VPS with unblocked egress 25 (Hetzner after verification, OVH, Vultr) works equally well — point mailcat at it via --proxy or just run mailcat on the VPS itself.

The HTTP-based checks (everything else) work fine from any network and do not require Tor.

Three checks (fastmail, intpl, onet) drive a real browser, because those providers only expose their availability API to page JavaScript. Pyppeteer downloads its own Chromium (~150 MB) on the first run, but on a slim Linux box that binary still needs system libraries that are usually missing:

[WARNING] Onet check failed: Chromium/browser issue (Browser closed unexpectedly:

On Debian/Ubuntu, install them once:

sudo apt-get install -y libnss3 libnspr4 libatk1.0-0t64 \
    libatk-bridge2.0-0t64 libatspi2.0-0t64 libxdamage1 libasound2t64 libxres1

(before Ubuntu 24.04 the t64 suffix is not used: libatk1.0-0, libatk-bridge2.0-0, libatspi2.0-0, libasound2)

Nothing else needs a browser. If you do not care about these three providers you can skip the libraries — the checks fail gracefully with the warning above and the rest of the run is unaffected.

This tool uses the following OSINT techniques:

• SOTL-2.2. Search For Accounts On Other Platforms
• SOTL-6.1. Check Logins Reuse To Find Another Account
• SOTL-6.2. Check Nicknames Reuse To Find Another Account

Looking for accounts rather than emails? Maigret searches 3000+ sites by username — same input, different output. There's a Telegram bot if you'd rather not install anything.

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