Why would they submit their own bitcoin address?
Good point, I think this is mass-protocol-dyslexia triggered by my original reply....
Unless you have some sort of outgoing-payments system where recipients get an e-mail like:
"
Subject: You've got coin!
OP owes you Bitcoin and wants to pay up. Just Click
<a href=blah.blah/blah.php?auth=huge_crypto_number>this</a>
link to start the process.
In which case I guess you really do need their address (triple checked to make sure I didn't get it backwards yet again, which would be pretty typical of me -- typically I always guess the wrong Boolean outcome no matter how many times I try to reverse my position until I draw some kind of ridiculously trivial Visio diagram
)