I thought too that kernel have nothing to do with mail headers and after many hours trying various things we did reboot with old kernel and mail headers was again there. I have no explanation why or what happened. It sounds crazy but it is so. I have no reason to lie here. I'm stressed out enough with angry customers on the phone and email.
I feel your pain, and we are here to help. I have a hunch whats happening, and if you can answer the questions below I'm sure we can figure this out.
I believe you said you were running the dazuko module, could you tell us what directories you configured dazuko to monitor?
Also, have you checked your mail servers error logs, and what errors do you see from your mail server?
Do you see any errors for your system logs when this was occurring, and what are those errors?
Could you elaborate why headers was striped immediatelly after kernal update and no more striped after reboot with old kernel?
Thats just it, the kernel doesnt have the capability to do this, so you're not crazy - its actually not the kernel, so this ha to be a correlative issue, not causational. As theres nothing in any Linux kernel that can or will open an email message and remove the headers, we can rule that out as the cause. But since its related, then this is likely because of a feature thats only available with that kernel, or its a module thats only available in that kernel. Now, this is just a hunch, but I bet this is a case where a component is crashing or failing and thats causing your headers to get mangled. As you said, this appears to only occur for you when you either run a secure kernel like the ASL kernel, or when you have certain kernel modules loaded.
If thats true, then I suspect this is either a bug in some mail server application, or a configuration problem with a kernel feature. It may be that your mail scanner is either doing something either insecurely (unlikely, but the logs will tell us if thats true) that its prevented from doing, it has a bug in it and its dying/crashing, or you have something configured on your system such as dazuko that is creating a conflict with whatever your mail scanner is doing.
This is all a guess, so if you could answer the questions then we'll have a real handle on this.