Mailcat explained: how a nickname can reveal your email
Mailcat answers a narrow question: if someone goes by a given nickname, which email providers have a mailbox with that name? This page explains what that reveals and how to keep your own address harder to guess. It is educational and defensive, not a guide to looking up other people.
Email address discovery by nickname. Project: github.com/sharsil/mailcat · License: Apache-2.0 · Last reviewed 2026-10-17
What is Mailcat?
Mailcat is a Python project by sharsil under the Apache-2.0 license, last pushed in September 2026. Its README lists 26 active providers covering more than 158 domains, with more checks kept in the code but disabled after providers changed. It says it works without notifying the user.
The weakness it relies on is the same one behind other email enumeration: mail servers, sign-up forms and recovery pages often answer differently for an address that exists. Repeating that check across many providers turns one nickname into a list of real addresses.
WhatsMyName Apps does not offer email enumeration. Our email tools are listed as coming soon and are not live.
Why it matters for your privacy
- If your email name matches your public username, anyone who knows your handle can find your inbox.
- A confirmed address is the starting point for phishing, spam and password-reset attacks.
- Linking a handle to an email can join accounts you meant to keep separate.
- You get no notification when someone checks.
How to protect yourself
- Do not reuse your public social media handle as the name part of your main email address.
- Use email aliases or forwarding addresses for sign-ups and public contact.
- Keep a private address for banking and account recovery that you never post.
- Turn on two-factor authentication with an app or security key on your email account.
- Use a unique password for your mailbox, stored in a password manager.
Mailcat vs WhatsMyName Apps
| Feature | Mailcat | WhatsMyName Apps |
|---|---|---|
| Input | Nickname (username) | Username |
| What it finds | Mailboxes with that name at 26 providers | Public profiles at that username |
| Email enumeration | Yes | Not offered (email tools coming soon) |
| Setup | Python package | Nothing to install. It runs in the browser |
| Privacy of the query | Runs on your machine | The username goes to our server only to run the check. It is not stored or logged |
Based on Mailcat's own documentation as of 2026-10-17. Tools change; the project page is the final word.
Pros and cons of Mailcat
Pros
- Shows how easily a reused nickname points to a real inbox.
- Open source, with each provider check documented in the code.
Cons
- Can be misused to find people's email addresses without consent.
- Checks break when providers change their sign-up or mail servers, and several are already disabled.
- Some checks need outbound mail access that many networks block.
Who Mailcat is for
Understanding Mailcat is useful for anyone who uses the same name everywhere, and for security teams who want to show staff how much a public handle gives away.
WhatsMyName Apps does not offer email or phone account enumeration. Our email and phone tools are marked coming soon. You can still check your own digital footprint by username.
Frequently asked questions
What does Mailcat do?
It takes a nickname and checks whether a mailbox with that name exists at the email providers in its list, per its README without notifying the owner.
Does WhatsMyName Apps offer a Mailcat-style email search?
No. We do not offer email enumeration. Our email tools are marked coming soon and are not live.
How do I stop my email being found from my username?
Pick an email name that differs from your public handle, use aliases for sign-ups, keep a private recovery address and turn on two-factor authentication.
Related tools and guides
- Holehe: Email account enumeration
- Epieos: Email and phone reverse lookup
- Ignorant: Phone number account check
- OSINT Framework: Directory of OSINT tools
- All OSINT tools compared
- OSINT username search · Reverse username lookup · Platform username checkers
- Username OSINT for beginners
Names and trademarks belong to their owners. WhatsMyName Apps is independent and not affiliated with or endorsed by Mailcat or its authors.