Many to many AND one to many association

I want create mini mail service in my website, but i have little
problem mapping assotiation.
I have two models User and Message, every message have one sender and
many recievers.
I map sender with user_id field in message and recievers with table
messagesusers with user_id and message_id fields.
In model message I add
belongs_to :user
has_many :users
and in messagesuser
belongs_to :user
belongs_to :message
I don't know what add in user model, i try with
has_many :messages
but doesn't work.
Thanks and sorry for my poor english

SaThot wrote in post #957715:

I have two models User and Message, every message have one sender and
many recievers.

First thing to understand is that there is no many-to-many association
here. As you said a Message belongs_to a user and Message has many
recipients, which are Users. So you basically just need to add a foreign
key to User to keep track of the one-to-many relation Message <--->>
User. We just need to do a bit of convention overriding to accomplish
this:

User
  has_many :messages

Message
  belongs_to :user
  has_many :recipients, :class_name => "User", :foreign_key =>
:recipient_message_id

Or if you want to make things more clear you could do:

Message
  belongs_to :sender, :class_name => "User", :foreign_key => :sender_id
  has_many :recipients, :class_name => "User", :foreign_key =>
:recipient_message_id