Receipt messages overflowing voicemail box

[adop]

One of our (or perhaps more) Unity users has a problem with “receipt” messages which overflow voicemail box. He gets them in high amount and he has to go to his mailbox and delete them all in order to access his messages. It is pretty annoying. We are running Cisco Unity 4.0.x. I found that if read receipt feature in Outlook is enabled it would cause this problem but this feature was not enabled on his Outlook. Any suggestions?
Thank you,

 

[adop]

These are read receipt messages that come in 2 flavors (this is what I hear when I check my voicemail box):

1. “your message was deleted without being read”
2. “your message was read ... and then gives me date and time”

Has anyone an idea what I could do to stop getting these?