Checks that a given character sequence (e.g. string) is a well-formed email address.
The specification of a valid email can be found in
and one can come up with a regular expression matching
all valid email addresses as per specification. However, as this
article discusses it is not necessarily practical to
implement a 100% compliant email validator. This implementation is a trade-off trying to match most email while ignoring
for example emails with double quotes or comments.