Main Status Codes


OK: Verification passes all checks including Syntax, DNS, MX, Mailbox, Deep Server Configuration and Grey Listing


Bad: Verification fails checks for definitive reasons (e.g. mail box does not exist)


Unknown: Conclusive verification result cannot be achieved due to mail server configuration or anti-spam measures.


Additional Status Codes

None: No additional information is available. This status differs from other additional status codes as it should not be retried (the result will not change).


AtSignNotFound: The required ‘@’ sign is not found in email address.


DnsConnectionFailure: The DNS connection failed.


DnsQueryTimout: The DNS service failed to respond (time-out). A typical example of this status code is when a DNS server on the target infrastructure is configured incorrectly.


DomainIsInexistent: The domain (i.e. the bit after the ‘@’ character) defined in the email address does not exist, according to DNS records. A domain that does not exist cannot have email boxes. A domain that does not exist cannot have email boxes.


DomainIsWellKnownDea: The domain is a well-known Disposable Email Address DEA.


There are many services available that permit users to use a one-time only email address. Typically, these email addresses are used by individuals wishing to gain access to content or services requiring registration of email addresses but same individuals not wishing to divulge their true identities (e.g. permanent email addresses).


DEA addresses should not be regarded as valid for email send purposes as it is unlikely that messages sent to DEA addresses will ever be read. DEA addresses should not be regarded as valid for email send purposes as it is unlikely that messages sent to DEA addresses will ever be read.


DoubleDotSequence: The email addresses domain contained double dots.


IpBlockDetected: An IP block has been detected.


InvalidAddressLength: The email address is an invalid length.


InvalidCharacterInSequence: The email address contains an invalid character.


MailboxFull: The mailbox is full.


Mailboxes that are full are unable to receive any further email messages until such time as the user empties the mail box or the system administrator grants extra storage quota.

Most full mailboxes usually indicate accounts that have been abandoned by users and will therefore never be looked at again.

We do not recommend sending emails to email addresses identified as full.


MailboxDoesNotExist: The mailbox does not exist. (100% confidence that the mail box does not exist.)


MailboxTemporarilyUnavaible: The mail server is operating Grey Listing. Whilst we endeavour to verify grey listed addresses, sometimes it is not possible whilst still offering timely verification results.


NoMxServersFound: There are no mail servers defined for this domain, according to DNS. (Email addresses cannot be valid if there are no email servers defined in DNS for the domain.)


ServerDoesNotSupportInternationalMailboxes: The server does not support international mailboxes.


International email boxes are those that use international character sets such as Chinese / Kanji etc. International email boxes require systems in place for Punycode translation. Where these systems are not in place, email verification or delivery is not possible. For further information see Punycode.


ServerIsCatchAll: The server is configured for catch all and responds to all email verifications with a status of Ok.


Mail servers can be configured with a policy known as Catch All. Catch all redirects any email address sent to a particular domain to a central email box for manual inspection. Catch all configured servers cannot respond to requests for email address verification.


SmtpConnectionFailure: The TCP connection to the target mail server failed.


SmtpConnectionShutdown: The target mail server prematurely terminated the connection.


SmtpConnectionTimeout: A timeout occurred whilst waiting for a connection to the target mail server.


SmtpConnectionRefused: The SMTP connection was refused by the remote server. This status code applies to all Office 365 mail server, stopping verification, as these mail servers all operate a catch-all policy.


Success: Successful verification. (100% confidence that the mail box exists.)


TooManyAtSignsFound: Too many ‘@’ signs found in email address. (Only one ‘@’ character is allowed in email addresses.)


Unknown: The reason for the verification result is unknown.


PossibleSpamTrapDetected: A possible spam trap email address or domain has been detected.


Spam traps are email addresses or domains deliberately placed on-line in order to capture and flag potential spam based operations. Our advanced detection heuristics are capable of detecting likely spam trap addresses or domains known to be associated with spam trap techniques.


We do not recommend sending emails to addresses identified as associated with known spam trap behaviour.

Sending emails to known spam traps or domains will result in your ESP being subjected to email blocks from a DNS Block List. An ESP cannot tolerate entries in a Block List (as it adversely affects email deliver-ability for all customers) and will actively refuse to send emails on behalf of customers with a history of generating entries in a Block List.