Mails are not being sent

I would be grateful if someone can help me step by step tp resolve this
I have my application on production environment.
I define the SMTP server settings on config/environments/production.rb

as follows:
config.action_mailer.raise_delivery_errors = true
config.action_mailer.delivery_method = :sendmail
ActionMailer::Base.default_url_options[:host] =

and nothing defined in my environment.rb related to the mails sending,
except the sender email as follow:
DEFAULT_MAILER = “[email protected]

When I trail the error log production.log, the log says that my emails
are sent successfully on production.
But the emails are not sending.
How can I figure out what the problem is.

Your quick response is highly appreciated.

Thanks alot.