在《Bitmessage: A Peer-to-Peer Message Authentication and Delivery System》
Behavior when the receiver is offline An object is a public key request, a public key, a person-to-person message, or a broadcast message. Objects are broadcast throughout a Bitmessage stream. We propose that nodes store all objects for two days and then delete them. Nodes joining the network request a list of objects from their peer and download the objects that they do not have. Thus they will receive all messages bound for them that were broadcast during the last two days. If a node is offline for more than two days, the sending node will notice that it never received an acknowledgement and rebroadcasts the message after an additional two days. It will continue to rebroadcast the message, with exponential backoff, forever. In the worst case, if a user is offline for n days, he must go back online and stay connected for n days (or connect once every two days for n days) in order to receive all of his messages.