After an upgrade of scalix you may find that the load of the server is quite high.  Its the Search and indexing service re-indexing all email for SWA. This is normal behavior.

While its normal, its certainly not desirable, especially if you've got a large mailstore or have upgraded during the day. To get around this high load you can throttle the indexing service.

vi /var/opt/scalix/XX/s/sys/general.cfg 

Add the following lines, the comments are just for reference.... 

# Throttle the mailbox indexing service to avoid system crash
# where xx and yy are per-CPU load averages. The IDX_MAXLOAD setting
# will stop the indexer from indexing any further messages when the
# per-CPU load average goes above the defined value. The indexer will
# not resume indexing until the per-CPU load average goes below the
# value defined by IDX_MINLOAD.
IDX_MAXLOAD=6
IDX_MINLOAD=2

Save and quit. Restart scalix to affect the change.

service scalix restart

Of course you can use your own values to suit your environment.