The following code cause a really strange error in production:
The specified string is not in the form required for an e-mail address.
Obviously it is!
After immediately leaping to the conclusion that .NET is crap and I should immediately start writing my own virtual machine, I decided to dig a little deeper:
8203 stands for U+200B or zero width space.
I guess that someone with a software testing background decided to get medieval on one of our systems.