One of the most frequently asked questions in the system is "Why are my contacts not adding to the campaign", let me give you a scenario here: -
You have 1000 contacts but:
A) When you add them to the campaign NONE of them come through and it says you are sending to 0 people
B) When you add them to the campaign you don't get the full 1000 but you get say 875 contacts instead that you can send to
Here are the possible reasons (and solutions!)
So, for A) when the system says that NONE of your contacts have been added, this is most likely due to none of them having the all important permission to email clicked. This is a tick box against each contacts which signals to the system that you have their permission (opt in) to get emails from you, if this isn't ticked then the system things you don't have permission.
This can easily be solved, here is a like to a guide on updating your contacts to have this permission nice and quickly! Click here for the Update Many Guide
For B) when you appear to be missing some contacts, that is normally due to a couple of reasons: -
1) Some of your contacts have email addresses but DON'T have the all important tick for email permission, this can easily be added either manually or by using the above "Update Many"
2) Sadly some people have unsubscribed or complained about your previous emails, this means they end up on your suppression list, which stops you from emailing them again from the system, as they have said they don't want to get your emails again
3) Some of the contacts might not have email addresses or they might not be valid IE instead of a full stop there's a comma
Those are the most common reasons