Of the fields the validation report includes, the ResultStatus field contains the exact status code returned by the hosted email validation service engine.
The possible values for this field includes the following:
The e-mail address was verified successfully up to the required level.
A quoted pair within a quoted word is not closed properly.
An unexpected quoted pair sequence has been found within a quoted word.
A new word boundary start has been detected at an invalid position.
An invalid character has been detected in the provided sequence.
The number of parenthesis used to open comments is not equal to the one used to close them.
An invalid sequence of two adjacent dots has been found.
The local part of the e-mail address has an invalid length.
An invalid folding white space (FWS) sequence has been found.
The at sign symbol (@), used to separate the local part from the domain part of the address, has not been found.
An invalid quoted word with no content has been found.
The email address has an invalid total length.
The domain part of the email address is not compliant with the IETF standards.
A timeout has occured while querying the DNS server(s) for records about the e-mail address domain.
Verification failed because of a socket connection error occured while querying the DNS server.
The domain of the e-mail address does not exist.
The e-mail address is provided by a well known disposable e-mail address provider (DEA).
A timeout has occured while connecting to the mail exchanger which serves the e-mail address domain.
A socket connection error occured while connecting to the mail exchanger which serves the e-mail address domain.
The mailbox for the e-mail address does not exist.
A connection error occurred while validating the mailbox for the e-mail address.
The external mail exchanger rejected the local sender address.
A timeout occured while verifying the existence of the mailbox.
The requested mailbox is temporarily unavailable.
This is not an indicator that the mailbox actually exists but, often, a message sent by external mail exchangers with greylisting enabled. To complete the validation of the address, the system re-process the verification multiple times with small delays (usually 5-10 minutes), until the server answers with a different message or the number of validations hits its limit.
The external mail exchanger does not support international mailbox names. To support this feature, mail exchangers must comply with RFC 5336 and support and announce both the 8BITMIME and the UTF8SMTP protocol extensions.
A timeout occured while verifying fake e-mail address rejection for the mail server.
The external mail exchanger accepts fake, non existent, e-mail addresses; therefore the provided e-mail address MAY be inexistent too.
A connection error occurred while verifying the external mail exchanger rejects inexistent e-mail addresses.
A timeout occured while connecting to the configured proxy server.
A timeout has occured while connecting to the HTTP server (webmail) which serves the e-mail address domain.
A socket connection error occured while connecting to the HTTP server (webmail) which serves the e-mail address domain.
One or more unhandled exceptions have been thrown during the verification process.