When you send out an email and something goes wrong with it being delivered it is usually returned to you or "bounced". Bounced emails can happen for various reasons, some of them being permanent and some of them being temporary.
Hard Bounces - Hard bounces happen when any of the SMTP servers down that the email address you used to send will just never work. One of the first reasons an email will not reach it's destination is that the domain name does not exist. The second reason is that the mailbox on the mail server for that domain just does not exist. Hard bounces are usually characterized by a 500-series error. When an email is returned with a 500 series error inside, Campaign Enterprise and Email Marketing Director will categorize these as hard bounces. Usually when a hard bounce like this occurs, you mark a hard bounce field in the corresponding database record, and then when you send using that list again you filter out any email records that have this hard bounce field marked. Since it is a permanent failure, there is no reason to try sending to that address again. Aside from other information you want to keep in that record, the email address is virtually useless.
Soft Bounces - When a returned email not a 500-series return code, it is assumed to be a temporary or soft bounce. These types of bounces usually mean the domain is good and the email box is valid but for some reason the email server is not accepting any emails for this address at the present time. The reasons can range from the mail box is full, the server is too busy, or the person has marked his account as being on holiday. In the case of soft bounces, it is ok to try again the next time you send using that list. There will come a time though when maybe too many soft bounces really means a hard bounce...where an email box is always full (maybe not in use). In this case, you many not want to filter soft bounces out until a certain point, say, you get 20 soft bounces for that email address. In that case, you can filter the email list to exclude any records that have over 20 soft bounces. Now this is very arbitrary so you will have to set the number of times a record can soft bounce before you remove it from the list. Many times, sending emails to these addresses over and over is ok because the destination mail server does see the email box as valid, just not reachable, and that is not a bad mark on you.
So, for many, they just worry about hard bounces because those are the ones they can get in trouble with concerning the big mail providers. I would recommend just ignoring the soft bounce recording but it is up to your companies conventions.
BTW: Hotmail just got transformed to a new mail service called OUTLOOK.COM. We will be following this change to see how it affects our customer's deliver ability so check back over the next few weeks.