The two checks this tool actually runs
Enter any email address and this checks two independent things. First, whether the address is correctly formatted - a valid structure with an @ symbol, a proper domain portion, and no illegal characters. Second, whether the domain after the @ sign actually has mail server (MX) records configured, meaning it's set up to receive email at all. Together these two checks catch the large majority of typos and clearly fake or placeholder domains.
What this can't tell you
Neither check confirms that the specific mailbox - the exact person or inbox before the @ sign - actually exists or is being monitored. Verifying a specific mailbox typically requires sending a real message or using a mail server's own address-verification protocol (SMTP verification), which most mail servers now deliberately restrict specifically to prevent spam harvesting and abuse.
Why checking both format and MX records matters
Format checking alone would pass an address like [email protected], since it's
structurally valid even though the domain doesn't exist or accept mail. Adding the MX record check catches
exactly that case - a well-formed address pointed at a domain that simply can't receive email, whether from a
typo in the domain or an intentionally fake placeholder address.
Practical uses
Quickly sanity-checking a list of email addresses before a mailing, catching an obvious typo a user made signing up for something, or confirming a company's email domain is actually configured to receive mail before relying on it for important communication.