White scrren while sending large emails

[eluser]Unknown[/eluser]
I am using CI 1.7 version.
I want to send large emails using loop. The server is dedicated one with most of unlimited feature.
Case: One page has list of emails about 10000, then check box on each, I select all emails then post them to another controller from where email to each member is sent in loop but this controller stays blank and stops. I select 500 emails at once it worked fine but not for larger email list.
Any solution? Please Help.