Rules: Joining a Custom league
ACCEPTING AN INVITATION TO A PRIVATE CUSTOM LEAGUE
Custom leagues are private and can only be joined if invited to play by the League Manager. All invitations are sent in the form of an e-mail that contains a unique URL. This unique URL is the ticket to play in the league. To accept the invitation, the URL must be clicked or copied and pasted into your browser's address field. Upon a successful join, your ESPN.com Member ID will be associated with a Team ID and you will become that team's owner.
NOTE: Only the league manager can invite people to play in a Custom league. If you are unable to find your invitiation from the League Manager or unable to find the e-mail, it is recommended that you contact your league manager ASAP so that he/she may resend the invitation to you before your draft day.