1. Do we really need to configure mail.smtp.user and mail.smtp.password information?
-> yes it it mandatory
2. What value should be maintained in Mail.from?
-> you can give any mail ID from which you want to receive the alerts.
3. Where can I check whether current java mail client service configuration is working or not (Similar to Test Email from SCOT)
->AFAIK, there is no way. If you dont configure the valid details then you should find some errors in the alertjob log details.
4. Where can I see these outgoing mail? (Like I can see outgoing mail in SOST)
->AFAIK, there is no such option. If your job executed successfully. then you should receive it immediately.
5. Where can I see Alert Messages in SAP PI 7.31 CBMA as previously we used to see them in Alert Inbox?
->you have a service "AlertRetrieveAPI". using wsnavigator you can query and fetch the alert information.