Running 0.4.2-stable with default skin. Seeing many (several hundred daily) 404's logged in Apache. Entries are always the same, other than the IP address and the ID(?) in the request:

xxx.xxx.xxx.xxx - - [14/Feb/2011:07:33:10 -0800] "GET /webmail/?_task=mail&_remote=1&_action=keep-alive&_t=1297697589810&_=1297697589810&_unlock=0 HTTP/1.1" 404 15

This is not consistent - many similar entries log as successful - i.e. 200. Any ideas what I should look for?