You have an email address, but you are not sure whether it is right. Perhaps a customer typed it into a form, or a message has bounced. Before sending again, check the spelling and the domain after the @ sign.
Start with the address format
An address needs a mailbox name and a domain. A missing @ sign, a space in the wrong place or an extra dot can make it unusable. Our email verification tool checks common address formats. It supports ASCII mailbox names and domain names that PHP can convert to Punycode. Some international mailbox formats are outside its scope.
Then look at the domain's mail records
MX records tell sending servers where a domain expects to receive mail. If the checker finds them, the domain has published mail routing instructions. It does not mean a particular person has an account there. Lower MX preference numbers are normally tried first.
A domain can also publish a Null MX record to say it accepts no email. That is different from a domain with no MX record at all. Without MX records, SMTP can fall back to the domain's address records. A fallback address still does not prove that a mail server is listening.
What about a timeout?
A DNS timeout is an incomplete check. It is not evidence that the address is bad. Try again later or compare the result using the MX lookup tool.
Confirm the person separately
For a signup or account change, send a confirmation link through your own email system and ask the person to use it. This checks access to the mailbox at that time. Our tool does not send messages, contact mail servers or claim that an inbox exists.
Technical reference: RFC 7505: Null MX records.