Under the configuration settings of the Odoo Purchase module, a new option is there,
’Receipt Reminder’. Receipt Reminder helps to remind the receipt date to your vendor.
After enabling this feature, create a purchase order. In the purchase order form,
below the receipt date, you can have a checkbox for ‘Ask Confirmation’. This is
for sending an email to your vendor for delivery confirmation. The receipt date
is the delivery date promised by the vendor to the expected arrival date of the
product. So on enabling ask confirmation and adding numbers days, say X, in the
specified field, an email can be sent to vendor X days before the receipt date for
confirming the delivery date.