Prerequisite to Config Database Mail

Step 1: Verify SQL Server Agent Service is Running:

Messages in Database Mail are sent by the SQL Server Agent. If the Agent is not running, the messages will be accumulated in the msdb database and sent when the Agent service gets started again.
Use the master..xp_servicecontrol system stored procedure to check the status of the SQL Server Agent process. If the Agent is stopped, you will want to start it in order to send messages through Database Mail.
USE master
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EXEC xp_servicecontrol N'QueryState', N'SQLServerAGENT';
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Database Mail Architecture:

Database mail is newly introduced concept in SQL Server 2005 and it is replacement of SQLMail of SQL Server earlier version.
The main purpose of Database Mail is sending e-mail messages from the SQL Server Database Engine to users. We can send a text message, query result, failure alerts, file as attachment.
The database mail can be used to notify users or administrators regarding events raised in SQL Server.
To send Database Mail, you must be a member of the Sys admin <or >DatabaseMailUserRole database role in the msdb database.