As per the OOB structure how we will identify the source email address of the created case record from incoming email

I assume what you're after is the mailbox that received the email that the case was created from. Correct? You can determine the mailbox that the case was created from by doing the following:

1. Read Case to get "Parent activity" column. This is the email that created the case.
2. Read from "Email message" where Activity = Parent Activity from the Case. This will give you the MailboxSyncSettings that the email is from as one of the columns. The MailboxSyncSettings record is the email account that received the email.
3. Read the MailboxSyncSettings record returned from #2 to get the details about the mailbox that the email was received from.

Ryan