select 

       iif('email@...' similar to '([_a-zA-Z\d\-\.]+@[_a-zA-Z\d\-]+(\.[_a-zA-Z\d\-]+)+)','ok','fail')

from rdb$database

Says 'invalid string' and 'invalid pattern', but the pattern it´s the same in other languages for validate email address.

Well, just a couple of general observations:

- there is no such thing as a regular expression that can validate an email address, at best you can get an approximation that works "quite often" but still gets it wrong sometimes

- there are dozens of languages all with slightly different rules for regular expressions, it's not a surprise if any non-trivial regular expression needs changing between languages, you just have to read the rules for the new language.

-- 
Tim Ward