The invention relates to a method for file delivery in a system capable of one-to-many transmission, the method comprising transferring one or more data blocks from a sender to at least one receiver, identifying a data block expected to be received but not received at all or incorrectly received at the receiver, and taking action to re-transmit said data block. In the method, said identification is performed on the basis of a block number, an encoding identifier and certain other identification information.