Many replies now to this so apologies if this is already covered.
There is something wrong with this tale. Wilful delay must mean that you have not attempted to deliver the mail, right? And why not?
You might be reprimanded for taking home a 'P739 parcel' that is too big to fit the deposit box but that is not wilful delay.
Yep, saturday is a problem for big packets. Some just don't bother taking them. Some of us do with the hope that the customer will be home or we can give it to a neighbour or hide them somewhere or in the last resort clearly endorse the mail and take home... Yep!
You cannot be sacked for that! But best not to risk things.
And who is IB and why were you checked???