DatabaseMail process is shutting down
I have had the same issue and I followed these steps to resolve that.


EXEC msdb.dbo.sysmail_help_queue_sp
and check if length > 0 then DELETE QUEUE items.
Use the following query to delete queue items:

DECLARE @GETDATE datetime
SET @GETDATE = GETDATE()
EXECUTE msdb.dbo.sysmail_delete_mailitems_sp 
@sent_before = @GETDATE;

GO

EXEC msdb.dbo.sysmail_start_sp, start the process and check.