If you want a record of messages sent and received, set
jabber-history-enabled to t. By default all messages to will
be saved to a global history file specified by
jabber-global-history-filename
(~/.jabber_global_message_log by default). If you prefer to
store your chats' history in per-contact files, you can set the
jabber-use-global-history variable to nil. When using
per-contact history, files are named by the contact JID and saved
under the directory specified by the variable
jabber-history-dir (default is ~/.emacs-jabber).
There is no facility for reading old messages yet, but just reading the file as text should be enough for many purposes.
When you open a new chat buffer and have entries in your history file,
the last few messages you recently exchanged with the contact in
question will be inserted. You can control how many messages with
jabber-backlog-number (by default 10), and how old messages
with jabber-backlog-days (by default 3 days).
If you worry about your history file(s) size, you can enable history
rotation feature by setting the variable
jabber-history-enable-rotation to t (default is
nil). This feature “rotates” your history files according to
the following rule: When jabber-history-size-limit (in
kilobytes) is reached, the history file is renamed to
<history-file>-<number>, where <number> is 1 or the smallest number
after the last rotation. For example, suppose you set the
jabber-history-size-limit variable to 512 and you chat with
your buddy foo@jabber.server using the per-contact strategy to store
history files. So, when the history file (foo@jabber-server)
reaches 512K bytes, it will be renamed to foo@jabber-server-1
and foo@jabber-server will be set empty. Next time
foo@jabber-server grows to 512K bytes, it will be saved as
foo@jabber-server-2 and so on. Although the example was
presented with the per-contact history file strategy, history rotation
works for both per-contact and global history logging strategies.