I had few issues with creating email addresses. I set ($[FirstName])(.)($[Lastname])@(somewhere.com) regular expression to the email address. I cannot set unique column on to email and it gives me error message saying that it cannot generate enough data. I am sure that data length and uniqueness is not an issue.
Also, if I removed the unique option it will generate only 969 records and failed mid of data generation due to unknown reason.