What causes this type of address in envelopes?

[Steve Campbell]

Matt Kettler wrote:
> Steve Campbell wrote:
>> I have a little problem with a from envelop address. All of the 
>> header addresses are normal type somebody at somedomain.com, but the 
>> envelop from address takes the form
>>
>> prvs=somebody=7848db996 at somedomain.com.
>>
>> The recipient is a little mad, because I had the address whitelisted 
>> using the normal type address and it used to work. They want me to 
>> whitelist it again. I guess I could resave my file, but....
>>
>> Is it a proxy, or one of those dang MS products? Any clues?
>
> It's the Simple Private Signature (prvs) part of a IETF draft Bounced 
> Address Tag Validation (BATV).
>
> Essentially, it's a way of dealing with fake bounce messages by always 
> using a mangled address when sending. Any bounce messages that come 
> back which are sent to the regular user address are obviously caused 
> by spam forgeries (or broken mailsystems) and can be dropped.
>
> The current draft spec can be found at:
> http://tools.ietf.org/html/draft-levine-mass-batv-02
>

Wow, that's some thick reading.

So, if this is what they are using, then a simple "reply" to one sent to 
one of my users should work, unless the sender has their expiry timeout 
way too short? It seems that whenever someone tries to reply to the 
original sender, on occasion, the message is not accepted due to an 
invalid user return.
(I could be wrong on the memory part of that statement - they may be 
trying to send to the "real" email address of the sender, not that prvs 
thingy).

I guess you can send to the real address if it's not a reply? Are these 
setups sometimes misconfigured?

Thanks for the pointer and the help.Still a little confused, as you 
might discern.

Steve