If people who use '+' on purpose are fewer than those who type it in error (who type bobsmith+ when they meant bobsmith0, then it might not be a good idea. The

If people who use '+' on purpose are fewer than those who type it in error (who type bobsmith+ when they meant bobsmith0, then it might not be a good idea. The entire argument I was trying to make was that what constitutes a "legal email address" is not always what you want to validate. That some providers allow using '+' isn't as important as the number of users that actually do. If some nontrivial number of users use + on purpose, then don't reject them.