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SMTP server probe

Find out whether a domain's mail server accepts any address (catch-all) and how it handles TLS.

Takes up to a minute. No email is sent.

Try:

How it works

We look up the domain's MX records (the servers that receive its mail) and connect to the preferred one on port 25, the way another mail server would. If it doesn't answer, we try the next.

We say hello (EHLO) and note the extensions the server offers. If it offers STARTTLS, we switch the connection to TLS (encryption) and check the server's certificate: who issued it, when it expires, and whether it matches the server's name.

Then we start a message to a random address that can't exist, such as mw-3f9a2c@example.com. A server that accepts it is a catch-all: it takes mail for any address, so you can't tell a real mailbox from a typo. We stop before sending anything, so no email is delivered.

Some servers slow down or refuse unknown visitors, so a probe can take up to a minute or end early. Try again later if it does.