The REGEXP function replaces each substring of the input string that matches the given regular expression, with the given replacement. Therefore you are simply replacing the matching conditions with the same one again.
If you would like to get the email from the string, you might consider using SPLIT function to delimit the string by whitespace, and get the email from the array that is created from the SPLIT function.
You can refer to the [Text Processing Functions](https://community.denodo.com/docs/html/browse/7.0/vdp/vql/appendix/syntax_of_condition_functions/text_processing_functions#split) section of the Virtual DataPort VQL Guide for more information.
Hope this helps!