how to identify the default mail configurations In SQL Server, we can setup multiple email configurations out of which only some were set to default. 

I have tried using the following query to get the list of accounts:

select *
from msdb.dbo.sysmail_profile p 
    join msdb.dbo.sysmail_profileaccount pa on p.profile_id = pa.profile_id 
    join msdb.dbo.sysmail_account a on pa.account_id = a.account_id 
    join msdb.dbo.sysmail_server s on a.account_id = s.account_id


Is there any way to identify the default mail configuration profile?
Add a join to msdb.dbo.sysmail_principalprofile and check the is_default column to identify the default profile:

SELECT *
FROM msdb.dbo.sysmail_profile p 
JOIN msdb.dbo.sysmail_principalprofile pp ON pp.profile_id = p.profile_id AND pp.is_default = 1
JOIN msdb.dbo.sysmail_profileaccount pa ON p.profile_id = pa.profile_id 
JOIN msdb.dbo.sysmail_account a ON pa.account_id = a.account_id 
JOIN msdb.dbo.sysmail_server s ON a.account_id = s.account_id;