Box I is the easy part. If you expect a tax reimbursement, make sure the taxman has your bank account number. If it is printed on the tax return, you don’t have to give it again, unless you want to change the number.
This is also where you can give your telephone number; you don’t have to give your email address anymore. The taxman still prefers to send letters to keep things official, but more and more they agree to correspond by email. However, in recent weeks we noticed that they went back to corresponding by mail and that it is as good as impossible to get an email address or a telephone number for your local taxman.