Is it possible?

[MickDoneDee]

To simplify matters of tracking whether someone has read your PM:

Step 1: When sending a new PM or replying to a PM ensure you check this option - Request a read receipt for this message. As soon as your PM is sent go to Track Messages. A record of it should appear as Unconfirmed Private Message Receipts.

When the recipient reads it a popup will appear asking them to confirm or cancel. If they confirm Track Messages will show that in Confirmed Private Message Receipts. If they cancel the popup then it will stay in Unconfirmed Private Message Receipts even though they read it!

To ensure that the PM is confirmed automatically when the recipient opens the PM do the following:

Step 2: Open each usergroup settings and find Can Deny Private Message Read Receipt Request. Select the No option and save the setting change. Do this for all usergroups because members may belong to multiple usergroups and the No setting in one usergroup will be overridden by a Yes in a secondary usergroup.

Now the recipient won't receive a popup to give them a choice to deny receipt. Receipt will be added to Track Messages automatically as soon as the PM is opened. Make sure you check Request a read receipt for this message when sending a PM otherwise no receipt will be logged in Track Messages. Unfortunately, this option is unchecked by default so you have to remember to check it when you send the PM.

A template hack can have Request a read receipt for this message checked by default.
In the pm_newpm template replace $checked[receipt] with

checked="checked"