Restrict GR before Delivery Date

I want to restrict that vendor supplies goods before the delivery date written on PO .i.e. system should give some error if goods are supplied before the scheduled delivery date mentioned in PO.

One way is to check data at your MIGO entry, is through SAP enhancments (Tcode : cmod).
I have implemented numerous checks for my end users (posting dates, movement types vs material types, mandatory fields under specific conditions, posting date deviation from today, total consumption per order etc).

Try enhancment MBCF0002 and component EXIT_SAPMM07M_001.

Through tcode SMOD you can find the available enhancments and function modules, go through the documentation and choose one. For MM inventory management the package is MB.

My system (4.7) returns the following list:

Exit name Short text
MB_CF001 Customer Function Exit in the Case of Updating a Mat. D
MBCF0002 Customer function exit: Segment text in material doc. i
MBCF0005 Material document item for goods receipt/issue slip
MBCF0006 Customer function for WBS element
MBCF0007 Customer function exit: Updating a reservation
MBCF0009 Filling the storage location field
MBCF0010 Customer exit: Create reservation BAPI_RESERVATION_CREA
MBCF0011 Read from RESB and RKPF for print list in MB26

With tcode CMOD create a project "Zxxx" and insert the choosen enhancement. Automatically its components will be added to your project.

Press the "Compoents" button and double click the function exit that you will change.

Now you should be looking at the source code of the function (abap editor). Take a look of the available internal tables that are imported.

Double click on the include ZX....... which does not exist and it will be created by you.

Add the source code needed to cover your validations.

Save and activate your project

Execute MIGO and check your enhancement.

Note: one problem I still haven't solved. I can use only ERROR messages not WARNINGS.