Irreversibly hash email addresses while preserving format/entropy
Test cases are very limited.  You might want to normalise equivalent addresses before hashing; for example, these addresses are all equivalent:


user@example.org
user@Example.Org
"user"@example.org


It's probably desirable that they hash to the same value.

Simply splitting on @ is naive - it's better to split on unquoted @, or more simply, just on the last @, given that DNS names don't contain @.

It's probably worth reading I Knew How To Validate An Email Address Until I Read The RFC.  After that, start looking for an email address parsing library for Python; I haven't used it, but it appears that Flanker will handle the parsing much more robustly than this code.