Mailservers respond to requests with smtp error codes which show the email does not exist or is invalid. We have compiled these codes and assign them a hard bounce value. This information is fed into our appending platform where we match against our intelligence where we place a value delimiter per email.
Technical bounce classification:
’emaildoesntexist’
‘domaindoesntexist’
‘relayerror’
‘invalidemail’
‘inactive’
According to the rfc logic:
http://tools.ietf.org/html/rfc3463
– 5.2.1 is ‘mailbox inactive’.
– 5.1.1 is always ’email doesn’t exist’.