"Authentication failed" when third party smtp server is used

Hello,
I am using action mailer to send mails. I need to use a third party
smtp server. The third party smtp server i am using is authsmtp.

    ActionMailer::Base.smtp_settings = {
    :address => "mail.authsmtp.com",
    :domain => "mydomain.com",
    :port => 2525,
    :authentication => "login",
    :user_name => "promo@mydomain.com",
    :password => "password for promo@mydomain.com"
}

when i try to send the mail, i get authentication failed error. but if i
change the :address to mail.mydomain.com everything works fine.
I want to use authsmtp to send mail

I think i also have to authenticate the authsmtp server.I have its
username and password. Where do i have to write that.

Any idea whats going wrong.
Please help
Thank you.

when i try to send the mail, i get authentication failed error. but if i
change the :address to mail.mydomain.com everything works fine.
I want to use authsmtp to send mail

I think i also have to authenticate the authsmtp server.I have its
username and password. Where do i have to write that.

You should be using that username and password in your smtp settings.

Fred