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Forwarding messages to a new identity
psyced has the ability of forwarding messages to you from an old account to your newer account. You can activate it by issuing /set id <uniform> where <uniform> is your new psyc://something/~you identification address that you figure out by watching your own profile (/x or /surf commands).
Setting your identity actually instructs your old UNI that it is no longer in charge of your identity...
See also: redirect.
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Forwarding from your identity to a client
The normal operation of the UNI, when a UNL (like a client) has linked to it, is to forward all incoming messages to it.
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Perfect forward secrecy
See Encryption for that.