You can enable database mail feature using Surface area configuration tool or using SP_Configure procedure.

use master
go
sp_configure 'show advanced options',1
go
reconfigure with override
go
sp_configure 'Database Mail XPs',1
--go
--sp_configure 'SQL Mail XPs',0
go
reconfigure
go


Using Surface Area Configuration
1. Select Surface area configuration for features

2. Go to database page and click on check box.