"ok or valid" - The server is saying that it’s ready to receive a letter to this address and no tricks are detected.
"error" - server is saying that delivery failed, but no information about email existence or availability.
"smtp_error" - an answer from the SMTP server is invalid or the server is responding with some internal error.
"smtp_protocol" - SMTP server allows us to connect, but closing the SMTP session before the email was verified.
"unknown_email" - server is saying that the delivery failed and the email does not exist.
"attempt_rejected" - delivery fail, reason similar to "rejected".
"relay_error" - delivery fails because of some relaying problem.
"antispam_system" - some anti-spam technology is blocking the verification process.
"email_disabled" - email account is suspended/disabled/limited and can't receive emails.
"domain_error" - email server or DNS for the whole domain is not installed or incorrect, so all emails are not deliverable.
"dead_server" - email server is dead, no connection to it.
"syntax_error" - syntax error in email address.
"unknown" - This often happens if the destination mail server is too slow or temporarily unavailable. In some cases, retrying your request after about 5-15 minutes will return a valid or invalid response. Unknown addresses don't count against your verification balance.
"Invalid" - An invalid email occurs when you attempt to send an email to an address that is formatted in a manner that does not meet internet email format standards or the email does not exist at the recipient's mail server.
"Accept all or Ok for all" - This is a domain setting where all emails on this domain will be reported as accept all or ok for all which makes it difficult to determine the validity of an email. Such addresses are commonly used by small businesses, government agencies, medical facilities, and educational institutions to ensure they receive all emails, even those with typos. While many of these emails are valid, some organizations use this setting as a security measure to prevent spam.
If you have your own email server with dedicated IPs, accepting all emails can be safe for sending, provided your email list is healthy. However, if you use a third-party email provider that requires a bounce rate below 4%, accepting these emails is not safe for sending.
"Disposable" - Disposable email addresses are temporary accounts that can be quickly created or discarded.
"Spam Traps" -an email address that is used to identify and monitor spam email. It is also a type of honeypot because it uses a fake email address to bait spammers.
"Invalid vendor response" - means our server did not receive any response from the server domain, we usually get this response from yahoo domains which our team is working on resolving now.