The four checks behind one address
Syntax comes first: one @ sign, a part before it of at most 64 characters, no spaces, no doubled or edge dots, and a domain that is a valid name. Quoted forms and bracketed IP addresses are rare and count as invalid here.
Next the domain is looked up in public DNS. A name that does not exist stops the check, since mail to it can never arrive. A domain that exists is asked for its MX records, the list of servers that take its mail.
The domain is then compared with open lists of disposable mail services and free mailbox providers, and the part before the @ is compared with common shared names such as info, sales and support. All of this uses DNS and lists. The mail server is never contacted.
What the answer tells you to do
Domain can receive mail: the address is written correctly, the domain exists and publishes mail servers, and no list matched. It is a reasonable address to keep on a form or a list, and the only proof beyond that is a message that gets through.
Mail to this domain looks risky: something matched, and the reason is printed under the answer. A disposable domain usually means the person wanted to avoid giving a lasting address. A role address such as info@ goes to a shared inbox, not one person. No MX record with an address record means mail would be tried at the domain itself, which many sites do not run.
Domain cannot receive mail: the domain does not exist, publishes a null MX that refuses all mail, or has no mail host and no address at all. Ask the person for another address.
A free provider such as a webmail service is reported but does not change the answer, because most people use one.
What a domain-level check cannot say
Passing every check means the domain is set up to take mail. It does not mean the mailbox before the @ exists, is active or belongs to the person who typed it. A mail server may accept an address that does not exist and drop the message later, or reject a real one.
The reliable test for one address is to send a message to it. A confirmation email with a link, or a delivered reply, tells you what no lookup can. For lists, use this check to remove dead, throwaway and misspelled domains first.
A resolver that fails to answer is reported as a failed check, never as a missing mail setup, so retry after a moment before you act on it.
Frequently asked questions
How do I check if an email address is real?
Start by checking that it is written correctly and that its domain has mail servers, which this page does. To know a specific mailbox exists, send a message to it and look for a bounce, or ask the person to click a confirmation link.
Can this tell me if the person behind the address is reachable?
No. It reads the domain, not the mailbox. A good answer says mail to the domain can be delivered somewhere, not that this person reads it.
What is a disposable email address?
It is an address from a service that hands out short-lived inboxes, so a visitor can get past a signup form without a lasting address. The page flags a domain when it appears on an open list of those services.
Why is a Gmail or Outlook address not marked risky?
Free webmail is how most people receive mail, so the page notes it as information and leaves the answer unchanged.
What if the check says the domain does not exist?
Look for a typo in the part after the @, such as gmial or a missing letter in the ending. A name that DNS cannot find cannot receive mail.