#Embedded vs link

#I'm looking for the fastest way to search a Newsletter document for a connected Email. So far I have used
#MongoMapper with one document for Newsletter and another for Email. This is getting really slow with +100k
#Emails.

#I was thinking maybe its faster to embed the emails in an array inside Newsletter
#since I'm really only interested in the email ('someemail@email.com')
#and not any logic around it.

#1) Is it possible at all to embed as much as 100k-500k emails in one document?
#2) Is Mongoid better/faster for this?

#I'm adding the email if it is not already in the collection by asking

    email = newsletter.emails.first(:email => 'someemail@email.com')
    unless email
        email = Email.new(:email => 'someemail@email.com', :newsletter_id => self.id)
        email.save
    end

#And I think this is where it all starts to hurt.

#Here is how they are connected
Class Newsletter
   include MongoMapper::Document
   many :emails
   ...
end

Class Email
   include MongoMapper::Document
   key :email,         String
   key :newsletter_id, ObjectId
   belongs_to :newsletter
end


#would love for any help on this :)