What's wrong with this RegEx for validating emails?

Question

Here\'s a regex for validating emails - \\S+@\\S+\\.\\S+, I didn\'t write it. I\'m new to Regular Expressions and do not understand them all that well.

Answer 1

What's wrong with the above RegEx?
The RFC822 standard for email addresses is very loose, so it is hard to find a terse regular expression that captures all possible valid emails. The matter is complicated by the fact that not every mail server/client enforces this standard, so the actual data might be

While you can certainly guess, or enforce a particular format, writing an ad-hoc expression is pretty much a guarantee that you will have either lots of junk email addresses or deny valid ones.

What's a good RegEx for validating emails?
This is the reference regex for validating against the RFC, its implemented as a perl module here, but is also the final listing in O'Reillys "Mastering Regular Expressions"

Mail::RFC822::Address