Email ???

[CH]

Hello everyone,

I am not sure what the exact name of it but I will try to explain it.

Say you reply to am email to a person and it comes back saying that you 
need to verify that you are a real person and not a spammer.

Is there anything out there similar to that under the GPL or free??

Hopefully I explained that right.  I would have used google but I do not 
know the exact name of it.

Thanks,
Will