Although the experience may be frustrating, re-registering expired domain names is perfectly legal, and thousands of domain names are "recycled" in this manner each day. If you did not intend to let your domain name expire and would now like to try to get it back, you do still have a few options:
Consider your legal options
If the domain name is non-generic (e.g. not a real word), you hold a matching trademark, and the new owner has no legitimate interest in the domain, then you may be able to win the domain through a legal challenge. Consulting a qualified trademark lawyer with experience in domain name disputes.
Explain the situation to the current owner
Sometimes all it takes is a polite E-mail or phone call to the current owner to get your domain back. Be very polite, explain the situation, and offer to reimburse the new owner for the transfer fees as well as their expenses in acquiring the domain.
Hire a broker to acquire the domain name
If the new owner is reluctant to give up the domain, your best option may be to negotiate the purchase of the domain. Using a professional domain broker can help ensure that you get the best possible price.
For additional information, you may want to reference: