To get to this page, go to Settings → Header Processing  → Receipts/Urgent Messages → Receipts tab

If VPOP3 sees a message header containing any fields in the Delivery Receipt Header fields box, then it will send a message to the address in that header field when the message is delivered to a user's email client. If you don't want VPOP3 to generate a delivery receipt, simply clear this box.

The Only generate Delivery Receipts for Local Messages option tells VPOP3 to only generate these receipts to local addresses, not to external email addresses.

 

If VPOP3 sees a message header containing any fields in the Transmission Receipt Header fields box, then it will send a message to the address in that header field when the message is sent to another SMTP mail server. If you don't want VPOP3 to generate a delivery receipt, simply clear this box.

The Only generate Transmission Receipts to local users option tells VPOP3 to only generate these receipts to local addresses, not to external email addresses.

The Don't send Transmission Receipts when LAN Forwarding option tells VPOP3 not to send transmission receipts when VPOP3 sends the message using LAN forwarding, but only to send them when it sends a message out to a remote mail server (SMTP relay server/smarthost, or MX mail server)

 

As there is no standard for header fields to request a receipt, you can customise the header fields which VPOP3 should look for here. Return-Receipt-To: is a common header field to indicate that a receipt is wanted, but there are others. If you look at the full headers of an example message which you have sent when asking for receipts, then that may show you which header field to look for.

You can use 'From' in either of these boxes if you want VPOP3 to always generate a receipt, but you should be careful when using this option.