Unfortunately, that looks like it's a bug. It is actually going to only 25 (the ones listed from the link). A temporary fix for this (we'll be fixing this in the code) is to modify the admin template email_nav.html in data/admin/templates. You need to change the line with the link:
to:
Adrian
Code:
<a href="admin.cgi?action=GMail::Admin::SendEmail::search_form">Code:
<a href="admin.cgi?action=GMail::Admin::SendEmail::search_form;mh=-1">Adrian