While applying, Long Running Sessions Detection Job on a production server, we start receiving alert that a session is taking more then 3 minutes. But what actually this session was doing. Here is the alert report.

sp_readrequest is a system stored procedure, which basically reads a message request from the the queue and returns its  contents.

This process can remain active for a time we have configured for parameter DatabaseMailExeMinimumLifeTime, at the time of database mail profile configuration. 600 seconds is the default value for this external mail process. According to BOL DatabaseMailExeMinimumLifeTime is the The minimum amount of time, in seconds, that the external mail process remains active.

This can be changed, at the time of mail profile configuration or you can just use update query to change this time.

UPDATE msdb.dbo.sysmail_configuration
SET paramvalue = 60 --60 Seconds
WHERE paramname = 'DatabaseMailExeMinimumLifeTime'

We have changed this to 60 seconds to resolve our problem.