Service Broker is message queuing for SQL Server. It is used for sending emails and through Database Mails. You can read about SQL SERVER – Difference Between Database Mail and SQLMail here. Service Broker is feature which provides facility to SQL Server to send an asynchronous, transactional message.
SQL SERVER – Difference Between Database Mail and SQLMail
In recent user group meeting in my city Ahmedabad, I have found that not every user knows difference between these two features of SQL Server. I do not blame any user for not knowing difference between Database Mail and SQLMail as this is very confusing sometime. I will try to explain this concept here.