Soft and Hard bounces

Soft Bounce: Soft bounces basically mean the email was  sent to the server, processed, but for some reason was returned to us.  Common reasons include: "user over quota," and "server temporarily  unavailable." 

****NOTE: If you're receiving an email returned into your own email  account noting that someone is on vacation or is out of the office, that  address is not necessarily getting noted as a soft bounce in Total  Send. 

Most of your recipients' servers should be set up to NOT report to  us that the address bounced. If they did, your recipient might want to  let their IT group know that they are getting taken off important  mailing lists while they are on vacation. 

Hard Bounce: A hard bounce basically means we sent your  email, and the recipient's server outright rejected it. Common reasons  include: "Account does not exist," and "domain does not exist." 

Our systems are 99.9% accurate at determining soft/hard bounces. However  very occasionally a false classification can occur. This only happens  as a result of the rarest of server responses, when our servers  misinterpret an error sent from the recipients server.