In some situations, you may want to mark a PO as "sent" without actually emailing a copy of the PO to your vendor. For example, if the PO was created due to receiving a partial order, the vendor already has a copy of your PO. In this case, you may not need to resend the PO for the items still missing.
To mark a PO as "sent" without emailing the PO to your vendor, first click the Send to Vendor button to the right of the PO.
A pop-up window will appear. Click the blue-button that says Mark as Sent (no email).
This will mark your PO as "sent" without actually sending it to the vendor.