Just found this in the message.log.
DB Error: insufficient permissions: UPDATE horde_datatree_seq SET id=LAST_INSERT_ID(id+1) [nativecode=1142 ** UPDATE command denied to user 'horde'@'localhost' for table 'horde_datatree_seq'] [on line 355 of "/home/httpd/html/horde/lib/Horde/DataTree/sql.php"]
Could not log message details to Horde_History. Error returned: DB Error: insufficient permissions [on line 67 of "/home/httpd/html/horde/imp/lib/Maillog.php"]
What should I do with it?