Hi,
A blank From: address can be interpreted in several ways.Email messages have both envelope addresses and addresses in the message headers. The envelope addresses are created during the SMTP conversation when a message is received. The SMTP protocol requires an envelope-from address that is non-null; therefore it is not possible to receive a message with a blank envelope-from address. The envelope-from address "<>" is a special case that is specifically used by mailers to send bounce messages. This is a signal to the receiving mailer that a bounce cannot be sent to that address; it is used to prevent mail loops from occurring.
The message headers, including the From: header, are all considered part of the message content and are not required to match the envelope addresses. This is used to good effect by list email, for example, where very long recipient lists are not included in the content From: header, but a list return address is often given instead. This is also used in spam and viruses to mislead recipients about the sender of the message.
I would recommend reviewing the below article to prevent invalid emails with empty senders.
http://www.cisco.com/c/en/us/support/docs/security/email-security-appliance/117799-problem-esa-00.html
Bounce verification would stop invalid bounce emails with empty sender while still allowing legitimate bounce emails. Adding a filter is also an option, however that would block all emails with empty senders.
Thank You!
Libin Varghese
