How does the Bounce Address Tag Validation (BATV) work?
This filter is designed to recognize Non-delivery Reports / Bounce mails which have been sent to fake e-mails and direct them elsewhere.
The filter determines if an e-mail address is real or fake directly before transmitting the mail.
The filter works incredibly fast and efficiently.
If an address is determined to be fake, the mail will be rejected immediately.
Activate the filter in the Configuration -> E-Mail Transport -> SMTP Settings -> BATV tab -> Enable BATV.
Here it is also possible to enter addresses which should not be tested by the BATV.
When a mail is sent, the sending address is given a signature.
Through this signature, the REDDOXX determines if incoming Non-delivery Reports are for mails originally sent by the REDDOXX.
When the BATV is enabled, only the envelope address will be tampered with. The mail itself will never be changed!
During the transmission of a mail, the envelope of the sender address will be changed from, for example, "firstname.lastname@example.org" to an address with the following syntax: "prvs=1838E5D28Aemail@example.com".
This signature address will be used if a Non-delivery Report is generated, and this signature will be tested by the REDDOXX upon arrival.
This test only takes place on mails without a sender address.
At this time, the following side effects of the BATV are known:
Some Greylisting applications do not accept the signature (very seldom).
It is possible that the sent mail will not be accepted by the destination mail server and the mail will be returned with an error message.
In these cases, the respective sender address should be registered in the "BATV exception addresses".
When POP3 clients send through the REDDOXX, the POP3 addresses need to be registered in the "BATV exception addresses".
The BATV filter does not work properly anymore together with MS Exchange Server since version 2007 because the Exchange Server do not reply anymore a Message Disposition Notification (MDN, e.g. out-of-office) to the envelope sender address (Mail From) but to the Return Path from the Mail Header, which does no contain a BATV signature at all.