If you are trying to do a form validation received from the client, or just a bean validation - keep it simple.
It's better to do a loose email validation rather than to do a strict one and reject some people, (e.g. when they are trying to register for your web service).
With almost anything allowed in the username part of the email and so many new domains being added literally every month (e.g. .company, .entreprise, .estate), it's safer not to be restrictive:
Pattern pattern = Pattern.compile("^.+@.+\\..+$");
Matcher matcher = pattern.matcher(email);
