setup send mail,sstmp ,postfix service for sending email by different applications as apticron

Dear Team

I am looking for setup the most reliable and available smtp service for debian for
sending  email notification from different applications as apticron.
As per experts request  I  opened new topic for configuration as  I  found that the 3 free  popular  smtp service are sendmail, postfix and ssmtp..
As I would like to know how to configure those smtp in details in order to send email notification
different applications as apticron.