Rules of validation of E-mail id

1. Every id should have only one @ symbol.
2. Every id should have minimum one dot ( . ) after @ symbol.
3. Dot and @ symbol should not come together  (side by side ) not allowed  eg. @.,.@,..
4. Space should not be inside E-mail id .
5. E-mail id should  not start with special char or digit.
6. E-mail id should not end with special char or digit.
7. Allowable special symbols are dot , @ and underscore ( _ ).