The mailtool does a user lookup of every site participant when it loads, even if the users are not to be displayed. If Sakai stores all user directory information in a local DB this extra performance hit may be negligible, but if you're configured to do an LDAP lookup (especially for a large course) the initial load time can be horrendous. This is a severe performance issue for large courses, one which prevents us from recommending the tool to our faculty.

It would be better if those lookups are only performed when a list is "expanded," and then have them cached. This would at least break it down into bite-sized pieces, and make the initial load time tolerable.