BATV (Bounce Address Tag Validation) Check
Not sure if this is already implemented in kerio but sounds like a good idea.
BATV is a mechanism wherein an outgoing Email server adds a tag to the Envelope From address of all outgoing Emails. For example, if an Email address goes out with From address as <firstname.lastname@example.org>, the Envelope From is changed to <prvs=SBDGAUJemail@example.com>, where 'SBDGAUJ' is the added tag. This tag is generated using an internal mechanism and is different for each email sent.
If any bounce is received by the Incoming email servers, they are checked to see if the Bounce address has the proper tag (in above case 'SBDGAUJ'). If not, the email is rejected.
BATV ensures that your Email users do not become a victim of bounce floods.
AMJAD JAMALI commented
I got this warning today when doing SPAM test against Kerio connect server