Email Gateway Defense is a pass-through service, accepting connections from a mail server, getting the initial RCPT TO line and connecting to the destination mail server. To understand how mail is delivered, an email message has two TO addresses, a HEADER TO address and an ENVELOPE TO (RCPT TO) address. The HEADER TO is read by users and mail clients but is not used for mail delivery. The ENVELOPE TO is used by mail servers to determine where the mail is being delivered. In the Email Gateway Defense Message Log, click the Show Details link in the message header for HEADER TO and ENVELOPE TO details.
In the below example:
- The HEADER TO information in the red box shows the email address (
recipient@testcudatest.com) to deliver the mail to. This is not used for the delivery of the message. - The green box is the information created by Email Gateway Defense when the mail is accepted and processed. This can be used to track messages in Email Gateway Defense.
- The ENVELOPE TO (RCPT TO) information in the blue box shows the email address (
recipient@testcudatest.com) given by the sending mail server. This is used to deliver the mail and shows the details about the delivery of the message.
Note: When the ENVELOPE TO information does not match the HEADER TO/CC information, it is usually because the sender did not include or removed email addresses in the reply message. The header information remains the same in the reply, but the mail is only delivered to the ENVELOPE TO set by the mail server.