Hotmail limits the number of contacts and safe senders.
Safe senders are different. They are anyone who you clicked on Mark as Safe. It is to get you to upgrade to a paying Hotmail account.
My advise is to forget Hotmail and to migrate to Google Mail - mail.google.com
This will give you 6.5GB of email sotrage and unlimited contacts/senders until you fill the space.
This is unlikely to happen, so gmail is a safe bet.