Permission to 'read' v 'receive'

Thanks for your response and sorry to leave this for so long. but can i just get some clarification.

Is the "read private messages' permission what turns on/off the ability for certain roles to be 'sent a message' ie, if Role=Authenticated does not have "Read private messages' should an Auth user
- show up in the auto-complete
- receive email notifications of the message that is sent.

I expected the answer to both of the above to be 'no' (well the second obviously should follow from the first)

and reading this question I posed back in Aug it would seem like that is what I was experiencing.

But just had it pointed out to me that on a Live site, even though Auth does NOT have 'read pm' permission
- they are selectable in the autocomplete
- they do get sent an email
but
- they do not have access to /messages.

Look forward to your clarification. If things are not behaving correctly on our site then I will endeavour to identify what might be messing with this.

We are using version

and just noticed that on the new user I created for testing purposes (Authenticated - for whom the Perms are
Admin PM - off
Read PM - off
Real All PM - off
Write PM - off
etc

when I go to user/%/edit it showing me

Private messages
Enable private messages - ON
Disabling private messages prevents you from sending or receiving messages from other users.
Receive email notification for incoming private messages - ON

Modules we are using
PrvMsg 7x_1.3
PrvMsg Email Notification
PrvMsg Filter
PrvMsg Limits
PrvMsg roles
PrvMsg Rules integration