Can I remove a "read receipt request" using PROPPATCH?

I am trying to process e-mail from a generic account that receives upwards of 200 e-mails a day.  I retrieve the e-mails using WebDAV, pull out the important stuff and then delete them from the account when I’m through with them.  However, when I delete the e-mails, end users have been complaining about getting “not read receipts” for said e-mails.  I’ve seen little information on the web about how to remove certain tags from the e-mail headers, but the only thing I’ve been able to do with a modicum of success is change the subject of an e-mail.  I need to totally remove “read receipt request” but I’m not sure HOW to do this with WebDAV and PROPPATCH…

Are there any suggestions or sites that anyone thinks to be helpful?