The user has told us to deposit to other address via email, for security reasons we wont reveal this address.
What kind of verification did you ask from the user before you were willing to change their destination address for $100k worth of bitcoin?
If I send BTC to you for the purpose of mixing them, I expect them to reach their destination specified in the letter of guarantee, not be intercepted during the mixing and be rerouted.
With changing the destination you did break your own letter of guarantee. I hope you are aware of what a dangerous precedence you are setting here.
What if for example their email was hacked and you were not communicating with the user that had originally deposited those funds to your mixer?
You're taking a huge risk by letting users change from addresses which you have signed.
Disclaimer: I have a working relationship with bitblender.io, my opinions are my own, and you can insult me for either of those two things as much as you like.