Money mail notification + Doc. number validation

This modification consinsts of two parts.

1) The system should send an Email notification to a particular user when New Real Income is created.

2) The system should not allow entering an Expense (real or planned (EDIT: ONLY REAL) with the same combination of Document number and Supplier withinone Project.
Description: Assume that we receive Purchase invoice. Project manager fills in this cost to the system. He has to pick the correct Project, Supplier and fill in the Document number (number taken from the Purchase invoice). Next (in the future) he forgets about it and tries to add the same cost in the same project again => System should not allow to do it (validates the Document number and Supplier).

Additional info (for clarification):

  1. The same Document number can be used in a different project or even in the same project - but only with different Supplier. The system should just block the combination of a Supplier+Document number within one project.
  2. Can the same number be used within one project on two different suppliers?  - YES
  3. When the user tries to add already entered Document number, the system should write following error message:
    "Cannot save the expense, selected Supplier + Document number is already entered."