Smtp mail problem

Hello guys,

Debugging the mail in gitlab get the following error.

Net::SMTPFatalError: 550 5.7.1 Client does not have permissions to send as this sender

    from /opt/gitlab/embedded/lib/ruby/2.3.0/net/smtp.rb:974:in `check_response'
    from /opt/gitlab/embedded/lib/ruby/2.3.0/net/smtp.rb:919:in `data'
    from /opt/gitlab/embedded/lib/ruby/2.3.0/net/smtp.rb:664:in `block in send_message'
    from /opt/gitlab/embedded/lib/ruby/2.3.0/net/smtp.rb:859:in `rcptto_list'
    from /opt/gitlab/embedded/lib/ruby/2.3.0/net/smtp.rb:664:in `send_message'
    from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/mail-2.7.0/lib/mail/network/delivery_methods/smtp_connection.rb:54:in `deliver!'
    from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/mail-2.7.0/lib/mail/network/delivery_methods/smtp.rb:101:in `block in deliver!'
    from /opt/gitlab/embedded/lib/ruby/2.3.0/net/smtp.rb:522:in `start'
    from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/mail-2.7.0/lib/mail/network/delivery_methods/smtp.rb:109:in `start_smtp_session'
    from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/mail-2.7.0/lib/mail/network/delivery_methods/smtp.rb:100:in `deliver!'
    from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/mail-2.7.0/lib/mail/message.rb:2160:in `do_delivery'
    from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/mail-2.7.0/lib/mail/message.rb:260:in `block in deliver'
    from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/actionmailer-4.2.10/lib/action_mailer/base.rb:543:in `block in deliver_mail'
    from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/activesupport-4.2.10/lib/active_support/notifications.rb:164:in `block in instrument'
    from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/activesupport-4.2.10/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
    from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/activesupport-4.2.10/lib/active_support/notifications.rb:164:in `instrument'
    from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/actionmailer-4.2.10/lib/action_mailer/base.rb:541:in `deliver_mail'
    from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/mail-2.7.0/lib/mail/message.rb:260:in `deliver'
    from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/actionmailer-4.2.10/lib/action_mailer/message_delivery.rb:85:in `deliver_now'
    from (irb):18
    from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/railties-4.2.10/lib/rails/commands/console.rb:110:in `start'
    from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/railties-4.2.10/lib/rails/commands/console.rb:9:in `start'
    from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/railties-4.2.10/lib/rails/commands/commands_tasks.rb:68:in `console'
    from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/railties-4.2.10/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
    from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/railties-4.2.10/lib/rails/commands.rb:17:in `<top (required)>'
    from bin/rails:9:in `require'
    from bin/rails:9:in `<main>'

Whats the problem here? Please help.
Thanks.