I tried to create a local Confluence user for someone who has an apostrophe in their name and email address. Many people's surnames contain apostrophes (e.g., "O'Brian") and in many cases people avoid creating email addresses that contain them. However, according to the standard for syntax in email addresses, the local part (the bit before the @ sign) can contain them (see RFC 6531 or http://en.wikipedia.org/wiki/Email_address). Therefore, I am prevented from creating a user account for a user with an apostrophe.