Eliminate false positives

The regex matched a lot of false positives since the word boundary is not set correctly and the dot is not escaped. For example this one `/\bnus.edu.sg/` does not only match evil@nus.edu.sg but also 
good@nus.edu.sg.com
nus-edu@sg.com
nus@edu.sgood.com
nusmedursg@good.net

I rearranged the code and eliminated the regex in favor of a simple comparison.