Redmine

Hello everyone
I'm a new member.
Please help me about send email to all members of project
I use function send news to all members of project:

• def news_added(news)
  redmine_headers 'Project' => news.project.identifier
  @author = news.author
  message_id news
  @news = news
  @news_url = url_for(:controller => 'news', :action => 'show', :id => news)
  mail :to => news.project.members.collect {|m| m.user}.collect {|u| u.mail},
  :subject => "[#{news.project.name}] #{l(:label_news)}: #{news.title}"
  end*

But my email of System only send maximum 50 mails at time.
While project has many members (about 200 members).
I want to ask, such as by changing the code to send mail to multiple times.
Each send to 50 people.
Thanks for your support.