offline message support
OTR should support (encryped/signed) offline messages, which is IMHO one of the crucial missing features of it (next to several security issues, already reported in the ticket system).
TextSecure and others have shown that this is doable even with PFS and DHs... just exchange the necessary secrets in advance when there's contact between the two peers and store them locally. Clients should be able to specify how many key exchanges are stored in advanced and/or for how many messages (perhaps in terms of number of bytes sent) these shall be used. OTR should make sure that the number of stored exchanged keys is refreshed once both peers are in actual contact. In case a peer should really send so many offline messages while the other side is not reachable, so that all previously exchanged keys ran out, the client should tell about that and block any further messages until new key exchanges have happened ... alternatively it may offer to continue on wit the last session key... or to send unencrypted.
(from redmine: created on 2015-11-11)