Partial searching with using email address in user picker fields

Problem Definition

We can search users with using email address in user picker fields.
However, only prefix searching is available and partial searching is not supported.

Suggested Solution

When it comes to some enterprise use cases, email addresses tend to be like,

• firstname.surname@example.com
• firstname_surname@example.com
• firstname-surname@example.com

It would be nice if we could do partial searching with using keywords which are separated by some special characters like ".", "_", "-". (Especially in the above examples, we want to search users with surname.)